[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$f32FOpuOoQw-IeOFdVVsqIJGi8VZfubaF6CkJ0g-1wpI":36,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":160,"$fucxFBm2ZjZfGSdmdRaSNGBI_F0jJme4f0GTvzUhQfL8":224},[4,8,12,16,20,24,28,32],{"title":5,"slug":6,"path":7},"About Microbeonline.com","about-microbeonline-com","\u002Fabout-microbeonline-com\u002F",{"title":9,"slug":10,"path":11},"About Me","about-me","\u002Fabout-microbeonline-com\u002Fabout-me\u002F",{"title":13,"slug":14,"path":15},"Advertise with Us","advertise-us","\u002Fadvertise-us\u002F",{"title":17,"slug":18,"path":19},"Privacy Policy","privacy-policy","\u002Fprivacy-policy\u002F",{"title":21,"slug":22,"path":23},"Authors","authors","\u002Fauthors\u002F",{"title":25,"slug":26,"path":27},"Microbes","microbes","\u002Fmicrobes\u002F",{"title":29,"slug":30,"path":31},"Books","recommended-books","\u002Frecommended-books\u002F",{"title":33,"slug":34,"path":35},"Tags","tags","\u002Ftags\u002F",{"type":37,"data":38},"blog",{"slug":39,"title":40,"description":41,"seoTitle":42,"seoDescription":42,"author":43,"createdDate":44,"lastUpdatedDate":44,"draft":45,"category":46,"image":42,"body":47,"faq":48,"commentsClosed":45,"tags":67,"related":69,"comments":156},"interferon-gamma-release-assay-igra-principle-procedure-interpretation","Interferon-Gamma Release Assay (IGRA): Principle, Procedure, and Interpretation","\u003Cp>How the IGRA (QuantiFERON-TB Gold, T-SPOT.TB) works, how to run it, and how to read positive, negative, and indeterminate results, including why it is not affected by BCG.\u003C\u002Fp>",null,"Acharya Tankeshwar","2026-08-31",false,"bacteriology","A previously BCG-vaccinated nurse has a 12 mm tuberculin skin test after a ward exposure. Is that induration from the vaccine or from real infection? This is the question the IGRA was designed to answer, and reading its result correctly is the difference between clearing a healthcare worker and starting unnecessary treatment.\n\n## What an IGRA measures\n\nAn interferon-gamma release assay is a blood test that detects a person's immune memory of [*Mycobacterium tuberculosis*](https:\u002F\u002Fmicrobeonline.com\u002Fmycobacterium-tuberculosis\u002F). When T cells that have previously met *M. tuberculosis* are re-exposed to its antigens in the tube, they release interferon-gamma (IFN-γ). The assay measures that release. A response means the immune system has seen the organism; it does not, on its own, tell you whether the infection is latent or active.\n\nLike the [tuberculin skin test](https:\u002F\u002Fmicrobeonline.com\u002Ftuberculin-skin-test-mantoux-test-principle-procedure-results\u002F), an IGRA is an indirect test. It is positive in both latent tuberculosis infection and active tuberculosis, so any positive result requires clinical evaluation for active disease before it is acted on.\n\n## Why the IGRA was developed\n\nThe tuberculin skin test has two long-standing weaknesses. It cross-reacts with the BCG vaccine, so a vaccinated person can have a positive skin test with no true infection, and it cross-reacts with some environmental non-tuberculous mycobacteria. It also requires the patient to return in 48 to 72 hours for the reading, and the induration measurement is operator-dependent.\n\nThe IGRA addresses the specificity problem directly. It uses antigens that are specific to the *M. tuberculosis* complex, mainly Early Secretory Antigen Target 6 (ESAT-6) and Culture Filtrate Protein 10 (CFP-10). These antigens are absent from the BCG vaccine strain and from most environmental mycobacteria. As a result, BCG vaccination does not cause a positive IGRA. The test is also completed on a single blood draw with no return visit.\n\n## The two IGRA formats\n\nTwo formats are in routine use, and they differ in what they measure.\n\n1. QuantiFERON-TB Gold (current version: QuantiFERON-TB Gold Plus) measures the concentration of IFN-γ released into plasma, reported in international units per milliliter (IU\u002FmL), using an ELISA readout. Whole blood is collected directly into antigen-coated tubes.\n2. T-SPOT.TB counts the number of individual T cells that release IFN-γ, using an ELISPOT method. Peripheral blood mononuclear cells are separated first, then exposed to the antigens, and the result is reported as the number of spot-forming units.\n\nBoth use the same ESAT-6 and CFP-10 antigen principle. QuantiFERON asks \"how much IFN-γ,\" T-SPOT asks \"how many responding cells.\"\n\n## Procedure\n\nThe value of an IGRA comes from its built-in controls, so the tube set matters more than the pipetting. For QuantiFERON-TB Gold Plus, **blood is drawn into four tubes:**\n\n1. **The Nil tube contains no antigen.** It measures the background IFN-γ already present in the blood, which is subtracted from the antigen result. A high Nil value signals a problem.\n2. **The two TB antigen tubes (TB1 and TB2)** contain the ESAT-6 and CFP-10 peptides. TB1 is designed to elicit a CD4 T-cell response; TB2 adds antigens that also elicit a CD8 T-cell response, which can matter in active and in some immunocompromised patients.\n3. The **Mitogen tube** contains a non-specific T-cell stimulant (phytohemagglutinin). It is a positive control: if the person's T cells are functional, this tube should always produce IFN-γ. A failed mitogen response tells you the immune cells could not respond at all, which is how an indeterminate result is identified rather than misreported as negative.\n\nTubes are incubated at 37 °C, plasma is separated, and IFN-γ is measured by [ELISA](https:\u002F\u002Fmicrobeonline.com\u002Felisa-principle-types-and-applications\u002F). The result is calculated from the antigen tubes after subtracting the Nil value.\n\n## Interpretation\n\nThis is the section that matters most, because the syllabus sets IGRA at the \"interpret\" bar, and because the interpretation queries are where the recoverable traffic sits.\n\n1. **Positive.** The IFN-γ released in a TB antigen tube, minus the Nil, exceeds the assay cutoff. This means *M. tuberculosis* infection is likely. It does not distinguish latent from active disease. A positive result always triggers clinical and radiological evaluation for active tuberculosis.\n2. **Negative.** The TB antigen response is below the cutoff and the Mitogen (positive control) responded normally. This makes *M. tuberculosis* infection unlikely, but it does not exclude it, particularly early after exposure or in significant immunosuppression.\n3. **Indeterminate.** This is the result students most often misread, and the one the controls exist to catch. It arises in one of two ways. Either the Mitogen tube failed to produce IFN-γ, meaning the T cells could not respond even to a strong non-specific stimulus, which points to immunosuppression, lymphopenia, or a processing\u002Fhandling error. Or the Nil tube IFN-γ was too high, meaning background reactivity was so elevated that a true antigen response could not be distinguished. An indeterminate result is not a weak positive or a weak negative; it means the test cannot be interpreted and usually needs to be repeated, with attention to sample handling and to the patient's immune status.\n\nA practical point that follows directly from the control logic: an indeterminate result in an apparently healthy person is more often a handling problem (delayed incubation, incorrect tube filling, poor mixing) than a true immune finding. Check the pre-analytical steps before concluding anything about the patient.\n\n## IGRA versus tuberculin skin test: a point-by-point comparison\n\nBoth the interferon-gamma release assay and the tuberculin skin test answer the same question: has this person's immune system met *Mycobacterium tuberculosis*? Neither answers the question that usually matters more, which is whether the infection is active. The two tests reach the same kind of answer by different routes, and the differences between those routes decide which test fits a given situation.\n\nThe tuberculin skin test injects purified protein derivative into the skin and measures the delayed immune reaction as induration at 48 to 72 hours. It happens in the body, in the skin, and it is read by eye. The IGRA takes blood, exposes the person's T cells to *M. tuberculosis*-specific antigens in a tube, and measures the interferon-gamma they release. It happens in the laboratory and is read by an instrument.\n\nThree differences follow from that, and they are the ones worth remembering.\n\n**Specificity and BCG.** The tuberculin skin test uses PPD, a crude mixture of many mycobacterial proteins, some of which are shared with the BCG vaccine strain and with environmental mycobacteria. A person vaccinated with BCG can therefore have a positive skin test with no true infection. The IGRA uses ESAT-6 and CFP-10, antigens that are absent from BCG and from most environmental mycobacteria, so BCG vaccination does not cause a positive IGRA. This is the single most important difference and the main reason IGRA was developed.\n\n**Logistics and the return visit.** The skin test requires two visits: one to place it, one to read it 48 to 72 hours later. A person who does not return cannot be tested. The IGRA needs a single blood draw with no return visit, which matters for populations unlikely to come back for a reading. Against that, the IGRA requires prompt laboratory processing; a delay in incubating the sample degrades the result, which the skin test does not have to worry about.\n\n**Reading and subjectivity.** The skin test induration is measured with a ruler and depends on the reader's technique and judgment, and on the patient's own reporting if the reader is not the same person who placed it. The IGRA readout is quantitative and instrument-based, with built-in positive and negative controls (the Mitogen and Nil tubes) that flag an uninterpretable result as indeterminate rather than letting it pass as a false negative.\n\nWhat the two share is just as important as where they differ. Neither test distinguishes latent infection from active disease. Both are positive in latent and active tuberculosis alike, and a positive result from either one requires evaluation for active disease before it is acted on. Neither should be used alone to diagnose active tuberculosis, which rests on direct methods: microscopy, culture, and nucleic acid amplification.\n\n**When to choose which.** The IGRA is preferred when the person has had BCG vaccination, because it is not confounded by it, and when a return visit is unlikely, because it needs only one draw. The tuberculin skin test remains a reasonable choice where IGRA is unavailable or unaffordable, in settings without prompt laboratory access, and in serial testing programs where its behavior over time is well understood. In young children, guidelines in many settings still favor or combine the skin test, where IGRA evidence is more limited.\n\n### IGRA vs tuberculin skin test in one table\n\n| Feature | Tuberculin skin test (Mantoux) | IGRA (QuantiFERON, T-SPOT) |\n| --- | --- | --- |\n| Sample | Intradermal PPD, read in the skin | Blood, tested in the laboratory |\n| Antigen | PPD (crude mix, shared with BCG) | ESAT-6, CFP-10 (specific to *M. tuberculosis*) |\n| Affected by BCG? | Yes, can cause false positive | No |\n| Affected by most environmental mycobacteria? | Yes | No |\n| Visits needed | Two (place, then read at 48-72 h) | One blood draw |\n| Reading | Induration measured by eye, operator-dependent | Quantitative, instrument-read, with built-in controls |\n| Built-in control for invalid result | None | Yes (Nil and Mitogen tubes give an indeterminate flag) |\n| Sample handling sensitivity | Low | Higher; needs prompt processing |\n| Distinguishes latent vs. active TB? | No | No |\n| Cost and lab needs | Low | Higher |\n\n### How to remember the difference\n\nOne antigen fact carries most of the comparison: **PPD is a crowd, ESAT-6 and CFP-10 are a shortlist.** PPD shares proteins with BCG, so the skin test reacts to the vaccine; the IGRA's shortlist antigens are not in BCG, so it does not. If you remember only that, you can reconstruct the specificity difference, the false-positive-with-BCG point, and the reason the IGRA exists.\n\nFor logistics: **skin test needs the patient to come back, IGRA needs the sample to move fast.** Each test has one weak link in its workflow, and they are opposite kinds.\n\n## Limitations\n\nAn IGRA cannot separate latent infection from active tuberculosis, so it cannot be used to rule active disease in or out. It can give false results in profound immunosuppression, where T cells may not respond even when infection is present. It is more expensive and more laboratory-intensive than the skin test and requires prompt sample processing, since delays in incubation degrade the result. It is not recommended as the sole test in young children in many guidelines, where evidence is more limited.\n\n## How to remember\n\nThe three tubes tell the whole interpretation story, so anchor the memory there rather than on a list of results:\n\n- **Nil = background.** If Nil is high, the test drowns in noise, indeterminate.\n- **TB antigen = the question.** High means infection likely.\n- **Mitogen = \"can these cells even respond?\"** If Mitogen is flat, the cells are not answering, indeterminate, not negative.\n\nThe single fact that separates IGRA from the skin test: **ESAT-6 and CFP-10 are not in BCG.** That one antigen fact is why BCG does not cause a positive IGRA, and it is the reason the test exists.\n\n## Key exam facts\n\n| Fact | Detail |\n| --- | --- |\n| What it detects | IFN-γ release by T cells sensitized to *M. tuberculosis* |\n| Key antigens | ESAT-6 and CFP-10 (absent from BCG and most environmental mycobacteria) |\n| Formats | QuantiFERON-TB Gold Plus (ELISA, measures IFN-γ concentration); T-SPOT.TB (ELISPOT, counts responding cells) |\n| BCG effect | None; IGRA is not affected by prior BCG vaccination |\n| Distinguishes latent vs. active? | No |\n| Positive | Antigen minus Nil above cutoff; infection likely; evaluate for active TB |\n| Negative | Antigen below cutoff with normal Mitogen; infection unlikely, not excluded |\n| Indeterminate | Failed Mitogen (positive control) or high Nil (background); repeat, check handling and immune status |\n| Positive control | Mitogen tube |\n| Negative control | Nil tube |\n\n## Where students get confused\n\n**\"Indeterminate means the patient is borderline.\"** No. Indeterminate means the assay could not be interpreted, almost always because the Mitogen control failed or the Nil background was too high. It is a statement about the test, not a statement about the patient's infection status. The first response is to check sample handling and repeat, not to treat.\n\n**\"A positive IGRA means active TB.\"** No. IGRA is positive in latent infection and in active disease equally. It cannot tell them apart. A positive result starts a work-up for active disease; it does not diagnose it.\n\n**\"IGRA is affected by BCG like the skin test.\"** The opposite is the whole point of the test. ESAT-6 and CFP-10 are not present in the BCG strain, so vaccination does not produce a positive IGRA.\n\n**\"A negative IGRA rules out TB.\"** It makes infection unlikely but does not exclude it, especially soon after exposure or in immunosuppression. Direct tests are needed to address active disease.\n\n## References\n\n- Tille PM. *Bailey & Scott's Diagnostic Microbiology.* 15th ed. St. Louis: Elsevier; 2022.\n- Procop GW, et al. *Koneman's Color Atlas and Textbook of Diagnostic Microbiology.* 7th ed. Philadelphia: Wolters Kluwer; 2017.\n- Leber AL, editor. *Clinical Microbiology Procedures Handbook.* 4th ed. Washington, DC: ASM Press; 2016. doi:10.1128\u002F9781683670438.CMPH\n- World Health Organization. *WHO consolidated guidelines on tuberculosis. Module 3: Diagnosis, tests for tuberculosis infection.* Geneva: WHO. 2025",[49,52,55,58,61,64],{"question":50,"answer":51},"\u003Cp>Does BCG vaccination affect the IGRA test?\u003C\u002Fp>","\u003Cp>No. The IGRA uses antigens (ESAT-6 and CFP-10) that are not present in the BCG vaccine strain, so prior BCG vaccination does not cause a positive IGRA. This is the main advantage of IGRA over the tuberculin skin test.\u003C\u002Fp>",{"question":53,"answer":54},"\u003Cp>Can an IGRA tell the difference between latent and active tuberculosis?\u003C\u002Fp>","\u003Cp>No. An IGRA is positive in both latent infection and active disease. A positive result means the person needs to be evaluated for active tuberculosis using clinical assessment and direct tests such as microscopy, culture, and nucleic acid amplification.\u003C\u002Fp>",{"question":56,"answer":57},"\u003Cp>What does an indeterminate IGRA result mean?\u003C\u002Fp>","\u003Cp>It means the test could not be interpreted, usually because the positive control (Mitogen tube) failed to respond or the background (Nil tube) was too high. It is not a weak positive or weak negative. The test is usually repeated after checking sample handling and the patient's immune status.\u003C\u002Fp>",{"question":59,"answer":60},"\u003Cp>What is the difference between QuantiFERON-TB Gold and T-SPOT.TB?\u003C\u002Fp>","\u003Cp>Both measure the same immune response using the same TB-specific antigens. QuantiFERON measures the concentration of interferon-gamma released using an ELISA. T-SPOT.TB counts the number of individual T cells that release interferon-gamma using an ELISPOT method.\u003C\u002Fp>",{"question":62,"answer":63},"\u003Cp>Should I choose IGRA or the tuberculin skin test?\u003C\u002Fp>","\u003Cp>IGRA is preferred when the person has had BCG vaccination or is unlikely to return for a skin-test reading, since it needs only one blood draw. The tuberculin skin test is still useful where IGRA is unavailable. Neither test diagnoses active tuberculosis on its own.\u003C\u002Fp>",{"question":65,"answer":66},"\u003Cp>What is the main difference between the IGRA and the Mantoux tuberculin skin test?\u003C\u002Fp>","\u003Cp>The biggest difference is BCG. The tuberculin skin test uses PPD, which shares proteins with the BCG vaccine, so a BCG-vaccinated person can test positive without true infection. The IGRA uses antigens (ESAT-6 and CFP-10) that are not in BCG, so vaccination does not cause a positive result. The IGRA is also a single blood test with no return visit, while the skin test needs a second visit to be read at 48 to 72 hours. Neither test can tell latent infection apart from active disease.\u003C\u002Fp>",[68],"mycobacteria",[70,102,132],{"slug":71,"title":72,"description":73,"seoTitle":42,"seoDescription":42,"author":43,"createdDate":74,"lastUpdatedDate":75,"draft":45,"category":46,"image":42,"faq":76,"tags":101},"mycobacterium-tuberculosis","Mycobacterium tuberculosis and Tuberculosis: Pathogenesis, Clinical Disease, and Diagnosis","\u003Cp>How \u003Cem>Mycobacterium tuberculosis \u003C\u002Fem>causes tuberculosis: why it survives inside macrophages, how the granuloma leads to latent and active TB, the clinical picture, drug-resistant TB, and how TB is diagnosed.\u003C\u002Fp>","2026-08-06","2026-08-25",[77,80,83,86,89,92,95,98],{"question":78,"answer":79},"\u003Cp>How does \u003Cem>Mycobacterium tuberculosis\u003C\u002Fem> cause disease?\u003C\u002Fp>","\u003Cp>It is inhaled and engulfed by alveolar macrophages, but instead of being killed it survives inside them by blocking the macrophage's killing machinery. The immune system walls it off in structures called granulomas, which contain the infection but also shelter living organisms that can reactivate later.\u003C\u002Fp>",{"question":81,"answer":82},"\u003Cp>What is the difference between latent and active TB?\u003C\u002Fp>","\u003Cp>Latent TB means the organism is present but walled off by the immune system: the person is infected, has a positive tuberculin or IGRA test, but is not ill and not infectious. Active TB means the organism has broken out and is causing disease; pulmonary active TB is infectious.\u003C\u002Fp>",{"question":84,"answer":85},"\u003Cp>Is latent TB contagious?\u003C\u002Fp>","\u003Cp>No. Only active pulmonary or laryngeal TB spreads through the air. People with latent TB do not transmit the organism.\u003C\u002Fp>",{"question":87,"answer":88},"\u003Cp>Why does tuberculosis affect the upper lungs?\u003C\u002Fp>","\u003Cp>Because \u003Cem>M. tuberculosis\u003C\u002Fem> is a strict aerobe and prefers the most oxygen-rich parts of the lung, which are the upper lobes. This is where reactivation TB typically causes cavities.\u003C\u002Fp>",{"question":90,"answer":91},"\u003Cp>Why does TB treatment take so many months and so many drugs?\u003C\u002Fp>","\u003Cp>Because the organism grows slowly, survives inside cells, and lies dormant in granulomas, so it cannot be cleared quickly. Several drugs are given together for months. Using one drug or stopping early causes relapse and drug resistance.\u003C\u002Fp>",{"question":93,"answer":94},"\u003Cp>What is MDR-TB?\u003C\u002Fp>","\u003Cp>Multidrug-resistant TB is tuberculosis resistant to at least isoniazid and rifampicin, the two most important first-line drugs. It needs longer treatment with more toxic second-line drugs. It arises mainly from incomplete or improper treatment.\u003C\u002Fp>",{"question":96,"answer":97},"\u003Cp>What is the Ghon complex?\u003C\u002Fp>","\u003Cp>The combination of the initial lung lesion of primary TB plus the involved draining lymph node. It is the pathological hallmark of primary (first-time) tuberculosis infection.\u003C\u002Fp>",{"question":99,"answer":100},"\u003Cp>Does the BCG vaccine prevent tuberculosis?\u003C\u002Fp>","\u003Cp>BCG mainly protects young children against the severe forms of TB (miliary TB and TB meningitis). Its protection against adult pulmonary TB is variable, so it does not reliably prevent the common adult form.\u003C\u002Fp>",[68],{"slug":103,"title":104,"description":105,"seoTitle":42,"seoDescription":42,"author":106,"createdDate":107,"lastUpdatedDate":44,"draft":45,"category":46,"image":108,"faq":109,"tags":131},"tuberculin-skin-test-mantoux-test-principle-procedure-results","Tuberculin Skin Test (Mantoux test): Principle, Procedure, Results","\u003Cp>How the Mantoux tuberculin skin test works: the delayed-type hypersensitivity principle, how to place and read the induration, the 5\u002F10\u002F15 mm cutoffs and why they differ by risk group, and its false positives and negatives.\u003C\u002Fp>","Nisha Rijal","2023-02-02","https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FMantoux_tuberculin_skin_test-1.jpg",[110,113,116,119,122,125,128],{"question":111,"answer":112},"\u003Cp>What does the tuberculin skin test detect?\u003C\u002Fp>","\u003Cp>It detects the immune system's memory response to \u003Cem>Mycobacterium tuberculosis\u003C\u002Fem>, not the bacteria themselves. A positive test means the person has been infected or exposed (or has had BCG), through a delayed-type hypersensitivity reaction that produces induration at the injection site.\u003C\u002Fp>",{"question":114,"answer":115},"\u003Cp>Why do you measure induration and not redness?\u003C\u002Fp>","\u003Cp>Because the firm, raised swelling (induration) is the actual delayed-type hypersensitivity reaction being tested. Redness (erythema) is not graded and can be misleading. The induration is measured in millimeters across the forearm.\u003C\u002Fp>",{"question":117,"answer":118},"\u003Cp>Why are there different positive cutoffs (5, 10, 15 mm)?\u003C\u002Fp>","\u003Cp>Because the threshold is set lower for people more likely to be infected or to progress to disease. HIV-infected people and recent TB contacts are positive at ≥5 mm, intermediate-risk groups at ≥10 mm, and low-risk people only at ≥15 mm. This balances detecting true infection against false positives.\u003C\u002Fp>",{"question":120,"answer":121},"\u003Cp>Does BCG vaccination affect the tuberculin skin test?\u003C\u002Fp>","\u003Cp>Yes. Prior BCG can cause a false-positive tuberculin test, which is an important limitation in countries where BCG is routine. Interferon-gamma release assays (IGRAs) are not affected by BCG, because they use antigens absent from the vaccine.\u003C\u002Fp>",{"question":123,"answer":124},"\u003Cp>Can the tuberculin test tell latent from active TB?\u003C\u002Fp>","\u003Cp>No. It shows infection or exposure but cannot distinguish latent infection from active disease. A positive result must be followed by clinical evaluation, chest X-ray, and, if needed, sputum tests to check for active TB.\u003C\u002Fp>",{"question":126,"answer":127},"\u003Cp>What causes a false-negative tuberculin test?\u003C\u002Fp>","\u003Cp>A weakened immune response, from HIV or other immunosuppression, very recent infection (within about 8 to 10 weeks), very young age, overwhelming TB, or certain viral illnesses and recent live-virus vaccination. In these situations an infected person may still test negative.\u003C\u002Fp>",{"question":129,"answer":130},"\u003Cp>What is the difference between the tuberculin test and IGRA?\u003C\u002Fp>","\u003Cp>Both measure the T-cell response to \u003Cem>M. tuberculosis\u003C\u002Fem>. The tuberculin test is a skin test read at 48 to 72 hours and is affected by BCG. IGRA is a single blood test, is not affected by BCG, and avoids reader subjectivity. Neither can distinguish latent from active TB.\u003C\u002Fp>",[68],{"slug":133,"title":134,"description":135,"seoTitle":136,"seoDescription":137,"author":43,"createdDate":138,"lastUpdatedDate":139,"draft":45,"category":140,"image":42,"faq":141,"tags":154},"elisa-principle-types-and-applications","ELISA Test: Principle, Types (Direct, Indirect, Sandwich, Competitive), Procedure, and Uses","ELISA (Enzyme-Linked Immunosorbent Assay) is the most widely used immunoassay for detecting antibodies and antigens. Learn all four ELISA types: direct, indirect, sandwich, and competitive. Explore step-by-step procedures, clinical applications (such as HIV, HBsAg, and dengue), and guidance on choosing the right type for your needs.","ELISA: Compare Four Types, Procedure, Results, and Applications","Compare direct, indirect, sandwich, and competitive ELISA formats, then review their reagents, procedures, result interpretation, and diagnostic uses.","2012-04-10","2026-08-21","immunology",[142,145,148,151],{"question":143,"answer":144},"Why is the indirect ELISA format used for HIV antibody detection rather than the direct or sandwich format?","\u003Cp>Indirect ELISA is the correct format for detecting patient antibodies (serology) because it uses a known antigen coated on the plate to capture the unknown antibody from patient serum, and then detects the captured antibody using a secondary enzyme-labeled anti-human IgG antibody.\u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>For HIV screening, the plate wells are coated with HIV antigens (HIV-1 and HIV-2 proteins) when patient serum contains anti-HIV antibodies, they bind to the plate-coated antigens. The enzyme-labeled anti-human IgG secondary antibody then binds to the captured human antibodies and generates the color signal. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>Direct ELISA would be inappropriate because the patient's own antibody cannot be enzyme-labeled, it is the unknown component being detected. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>Sandwich ELISA would be inappropriate because it detects antigens by capturing them between two antibodies, whereas HIV serology aims to detect the patient's antibody response. \u003C\u002Fp>\u003Cp>\u003C\u002Fp>\u003Cp>The indirect ELISA format has an additional advantage for clinical serology: the same enzyme-labeled anti-human IgG secondary antibody can be used for any antigen-antibody system, reducing the need to produce a separate enzyme-labeled antibody for every pathogen tested.\u003C\u002Fp>",{"question":146,"answer":147},"What is the hook effect in sandwich ELISA and how can it cause a false negative?","The hook effect is a false negative that happens in sandwich ELISA when antigen is so abundant it saturates the capture and detector antibodies separately, so most antigen molecules bind only one antibody and the sandwich bridge never forms. The signal drops even though the sample is loaded with antigen. It is suspected when a patient with strong clinical features has an unexpectedly low or negative result (classically very active hepatitis B with high HBsAg, or tumor markers at very high levels). The fix is to dilute the sample and retest, which breaks the antigen excess and restores the sandwich. This is one of two opposite false negatives in ELISA; for how it contrasts with the window-period false negative in indirect ELISA, see \"Where Students Get Confused\" above.",{"question":149,"answer":150},"How do 3rd-generation and 4th-generation HIV ELISA kits differ, and what is the clinical significance?","Third-generation HIV ELISA kits detect anti-HIV IgG and IgM antibodies only, using an indirect or capture ELISA format. They cannot detect HIV p24 antigen. Their window period is approximately 22–28 days from infection to detection. Fourth-generation HIV combination ELISA kits simultaneously detect both anti-HIV antibodies (using the indirect ELISA component) AND HIV p24 antigen (using the sandwich ELISA component) in a single well. Because p24 antigen appears in blood 10–12 days after infection — well before antibodies develop — 4th-generation combo tests have a window period of approximately 15–20 days, reducing the false-negative window by approximately 7–10 days compared to 3rd-generation tests. This seemingly small reduction has significant public health implications: people tested during early acute HIV infection (when viral loads are highest and infectivity is greatest) are more likely to receive a true-positive result with 4th-generation testing, allowing earlier diagnosis, treatment initiation, and prevention of onward transmission. Current WHO and national guidelines in most countries recommend 4th-generation combo tests as the standard for HIV diagnosis wherever available.",{"question":152,"answer":153},"Does \"direct ELISA\" mean it detects antigen and \"indirect ELISA\" mean it detects antibody?","No, and this is a common misunderstanding. The words direct and indirect describe how the enzyme label reaches the target, not whether an antigen or an antibody is being detected. In direct ELISA the enzyme is attached to the primary antibody that binds the target. In indirect ELISA the enzyme is on a secondary antibody that binds the primary antibody, adding an amplification step. It is true that in clinical practice indirect ELISA is used mainly to detect patient antibodies (serology) and sandwich ELISA to detect patient antigens, but that is a matter of how each format is applied, not what the prefixes direct and indirect mean. To decide what a given ELISA detects, look at what is coated on the plate and what unknown is being captured from the sample.",[155],"immunoassays",{"enabled":157,"threads":158,"total":159},true,[],0,[161,167,174,181,187,192,198,203,209,212,218],{"slug":162,"name":43,"description":163,"image":164,"body":165,"postCount":166},"acharya-tankeshwar","Editor-in-chief","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Ftankeshwar-acharya-author-microbeonline.jpg","***Tankeshwar Acharya, MSc (Medical Microbiology)***\n\n*Tankeshwar Acharya is an Assistant Professor in the Department of Microbiology at Patan Academy of Health Sciences (PAHS), Nepal, where he has been teaching and practicing clinical microbiology for over 14 years. He is the founder of Microbe Online, one of the leading free microbiology education resources on the web, covering bacteriology, mycology, parasitology, immunology, and clinical laboratory diagnostics written from direct experience in both the classroom and the diagnostic laboratory.*",489,{"slug":168,"name":169,"description":170,"image":171,"body":172,"postCount":173},"ashma-shrestha","Ashma Shrestha","SEO Copywriter and Science Communicator\nKathmandu, Nepal","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fashma-shrestha.png","Ashma Shrestha holds a Master of Science in Medical Microbiology from the Institute of Science and Technology (IOST), Tribhuvan University, Nepal, where she developed a strong foundation in virology, molecular biology, and diagnostic microbiology.\n\nShe now works as an SEO Copywriter at Resolution Digital, where she combines her scientific training with research-driven content strategy. She is certified in Google Analytics and Google Business Profile (GBP), and brings a data-informed approach to science communication writing content that is not only accurate but structured to reach and serve the students who need it most.\n\nAt microbeonline, Ashma contributes articles primarily in virology and molecular biology, areas she finds most compelling for their mechanistic depth and their growing clinical relevance. Her writing reflects the same standard the site is built on: factual rigor, clear explanation of the *why* behind microbiology concepts, and content that helps students move from memorization to genuine understanding.\n\nShe is passionate about making complex microbiological concepts accessible without sacrificing accuracy; a skill that sits at the intersection of her scientific training and her professional work in content and SEO.",79,{"slug":175,"name":176,"description":177,"image":178,"body":179,"postCount":180},"sushmita-baniya","Sushmita Baniya","Author \u002F Contributor","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fsushmita-baniya-1.png","Sushmita Baniya holds an M.Sc. in Medical Microbiology from Tribhuvan University (National College), with a research focus in Genetics and Molecular Biology. She is actively involved in teaching and research in the field of microbiology.",26,{"slug":182,"name":183,"description":177,"image":184,"body":185,"postCount":186},"samikshya-acharya","Samikshya Acharya","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fsamikshya-acharya.jpeg","Samikshya Sharma completed her postgraduate studies in Medical Microbiology at the Central Department of Microbiology, Tribhuvan University, Nepal. She contributes to Microbeonline with the goal of making foundational and clinical microbiology concepts clear and useful for students in medical, laboratory science, and allied health programs.",20,{"slug":188,"name":189,"description":177,"image":42,"body":190,"postCount":191},"alisha-tripathi","Alisha Tripathi","Alisha Tripathi holds an M.Sc. in Medical Microbiology from National College, Tribhuvan University. With over a year of teaching experience, her academic interests span Molecular Biology, Immunology, and Genetics.",6,{"slug":193,"name":194,"description":195,"image":42,"body":196,"postCount":197},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor","Aastha Shrestha is a Biotechnology graduate with an M.Sc. from National College, Tribhuvan University. Her academic interests center on Molecular Biology and Immunology; two fields that are increasingly converging in modern diagnostic and clinical microbiology. \n\nShe contributes to Microbeonline with the goal of making complex concepts in these areas approachable and exam-relevant for students across medical, biotechnology, and laboratory science programs.",9,{"slug":199,"name":200,"description":201,"image":42,"body":42,"postCount":202},"guest-author","Guest Author","Guest Author \u002F Contributor",1,{"slug":204,"name":205,"description":177,"image":206,"body":207,"postCount":208},"srijana-khanal","Srijana Khanal","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fsrijana-khanal-1.png","Srijana Khanal is a microbiology educator with nearly a decade of teaching experience, including her role as faculty in the Microbiology Department at National College, NIST. \n\nHer time in the classroom has given her a clear sense of where students struggle and what explanations actually work, a perspective that directly shapes how she writes.\n\nHer academic interests span Immunology, Genetics, Basic Sciences, and Research Methodology, and she brings the same rigor to her writing that she brought to teaching. Alongside academic writing, she has a passion for creative writing -- an instinct that shows in her ability to make dense scientific material readable without sacrificing accuracy.\n\nShe contributes to Microbeonline to extend her teaching reach beyond the classroom, helping medical and laboratory science students across the region build a stronger foundation in microbiology.",15,{"slug":210,"name":211,"description":201,"image":42,"body":42,"postCount":202},"dr-poonam-acharya","Dr. Poonam Acharya",{"slug":213,"name":106,"description":214,"image":215,"body":216,"postCount":217},"nisha-rijal","Microbiologist and AMR Specialist Kathmandu, Nepal","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fnisha-rijal-1.png","Nisha Rijal is a microbiologist with nearly 15 years of frontline diagnostic and surveillance experience at the National Public Health Laboratory (NPHL), national reference laboratory under the Department of Health Services, Nepal. She currently works as an AMR Support Officer at the World Health Organization (WHO), Nepal, where her work focuses on strengthening antimicrobial resistance surveillance systems and translating AMR data into actionable public health response.\n\nHer research, published in peer-reviewed journals and cited over 220 times, spans some of the most clinically significant infectious disease challenges in Nepal and South Asia: antimicrobial resistance trends in *Vibrio cholerae* across an 11-year national surveillance dataset, sero-epidemiology of scrub typhus in patients with acute febrile illness, lower respiratory tract infections in HIV-positive patients, and gonococcal resistance surveillance. She was a contributor to Nepal's National Antimicrobial Resistance Containment Action Plan, a foundational policy document for AMR governance in Nepal. You can find list of [Nisha Rijal's article here in Google Scholar.](https:\u002F\u002Fscholar.google.com\u002Fcitations?user=N-Ruq54AAAAJ&hl=en)\n\nThis depth of experience is visible in her writing at Microbeonline. Her 53 published articles cover bacteriology, parasitology, mycology, immunology, and laboratory techniques, and are consistently among the most detailed and clinically grounded content on the site. She brings to every article the same standard that national reference laboratory work demands: methodological precision, awareness of real diagnostic constraints, and an understanding of what results actually mean for patient care in resource-limited settings.\n\nHer areas of particular expertise include antimicrobial susceptibility testing and resistance mechanism detection, quality assurance in clinical microbiology, and laboratory-based infectious disease surveillance.\n\n---\n\n*Nisha Rijal contributes to Microbeonline in a personal capacity. Her views and writing do not represent the positions of the World Health Organization or any other institution.*",54,{"slug":219,"name":220,"description":221,"image":222,"body":223,"postCount":202},"padma-shrestha","Padma Shrestha","Author","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fpadma-shrestha.png","Padma Shrestha is from Kathmandu, Nepal. She has completed Masters degree in Medical microbiology from Tribhuvan University. She has great interest in Microbiology and Molecular Biology.",[225,232,238,243,248,253,256,260,264,269,273,278,282,287,292,296,300,304,309,314,318,322,326,329,333,337,341,345,350,355,359,363,367,372,376,380,384,388,392,396,400,404,408,412,416,420,424,428,433,437,441,445,449,453,457,461,465,469,473,477,481,485,489,493,497,501,505,509,512,516,519,522,525,528,531,534,537,540,543,546,549,552,555],{"slug":226,"name":227,"description":228,"image":229,"body":230,"postCount":231},"gram-negative-cocci","Gram-Negative Cocci and Coccobacilli","Neisseria, Moraxella, Haemophilus and related gram-negative coccal organisms","https:\u002F\u002Fassets.microbeonline.com\u002Ftags\u002Fgram-negative-cocci.png","# Gram Negative Cocci\n\nNeisseria gonorrhoeae, Neisseria meningitides, Moraxella catarrhalis, and other Neisseria spp. are clinically relevant gram-negative cocci.\n\nN. gonorrhoeae is the leading cause of sexually transmitted disease whereas N. meningitides is a leading cause of fatal bacterial meningitis.",14,{"slug":233,"name":234,"description":235,"image":42,"body":236,"postCount":237},"microscopy","Microscopy","Microscope types, components, and microscopy techniques","These are list of blog posts related to microscopy. ",12,{"slug":239,"name":240,"description":241,"image":42,"body":42,"postCount":242},"gram-positive-cocci","Gram-Positive Cocci","Staphylococcus, Streptococcus, Enterococcus, Micrococcus — organisms, diseases, and identification tests",11,{"slug":244,"name":245,"description":246,"image":42,"body":42,"postCount":247},"gram-negative-rods","Gram-Negative Rods (Other than Enterobacteriaceae)","\u003Cp>Gram negative rods other than members of Enterobacteriaceae family such as  Pseudomonas, Acinetobacter and related organisms\u003C\u002Fp>",5,{"slug":249,"name":250,"description":251,"image":42,"body":42,"postCount":252},"gram-positive-rods","Gram-Positive Rods","Bacillus, Clostridium, Listeria, Corynebacterium, Actinomyces and related organisms",8,{"slug":68,"name":254,"description":255,"image":42,"body":42,"postCount":237},"Mycobacteria","Mycobacterium tuberculosis, leprosy, atypical mycobacteria, and acid-fast organism diagnosis",{"slug":257,"name":258,"description":259,"image":42,"body":42,"postCount":237},"anaerobic-bacteriology","Anaerobic Bacteriology","Anaerobic organisms, anaerobic culture methods, and anaerobic infection diagnosis",{"slug":261,"name":262,"description":263,"image":42,"body":42,"postCount":237},"enterobacteriaceae","Enterobacteriaceae","Identification, differentiation, and clinical significance of Enterobacteriaceae family members",{"slug":265,"name":266,"description":267,"image":42,"body":42,"postCount":268},"spirochetes","Spirochetes","Treponema, Leptospira, Borrelia and spirochetal infections",7,{"slug":270,"name":271,"description":272,"image":42,"body":42,"postCount":231},"food-microbiology","Food Microbiology","Food-borne pathogens, food safety, spoilage, and preservation",{"slug":274,"name":275,"description":276,"image":42,"body":42,"postCount":277},"antimicrobial-susceptibility-testing","Antimicrobial Susceptibility Testing","Methods for testing antibiotic susceptibility in clinical microbiology",21,{"slug":279,"name":280,"description":281,"image":42,"body":42,"postCount":231},"antimicrobials-moa-amr","Antimicrobials (MOA & AMR)","Mechanisms, detection, and clinical significance of antimicrobial resistance",{"slug":283,"name":284,"description":285,"image":42,"body":42,"postCount":286},"sterilization-disinfection","Sterilization and Disinfection","Methods of sterilization and disinfection in healthcare and laboratory settings",10,{"slug":288,"name":289,"description":290,"image":42,"body":42,"postCount":291},"specimen-collection-transport","Specimen Collection and Transport","Collection, handling, and transport of clinical specimens for microbiological testing",27,{"slug":293,"name":294,"description":295,"image":42,"body":42,"postCount":277},"bacterial-structure-physiology","Bacterial Structure and Physiology","Bacterial cell structure, growth, physiology, and environmental factors affecting growth",{"slug":297,"name":298,"description":42,"image":42,"body":299,"postCount":191},"horizontal-gene-transfer","Horizontal Gene Transfer","Articles related to **Horizontal Gene Transfer**",{"slug":301,"name":302,"description":42,"image":42,"body":303,"postCount":286},"chromatography","Chromatography","Information about chromatographic techniques.",{"slug":305,"name":306,"description":307,"image":42,"body":308,"postCount":268},"electrophoresis","Electrophoresis","Information about Electrophoresis Techniques ","Detailed information  about Electrophoresis Techniques ",{"slug":310,"name":311,"description":312,"image":42,"body":313,"postCount":191},"pcr-techniques","PCR Techniques","Information about various types of Polymerase Chain Reaction Techniques ","More detailed information about various types of Polymerase Chain Reaction Techniques ",{"slug":315,"name":316,"description":317,"image":42,"body":42,"postCount":191},"bacteriophage","Bacteriophage","Description about Bacteriophage.",{"slug":319,"name":320,"description":321,"image":42,"body":42,"postCount":191},"malaria","Malaria","It is the collections of articles regarding malarial disease. ",{"slug":323,"name":324,"description":325,"image":42,"body":42,"postCount":191},"anaerobic-culture-techniques","Anaerobic Culture Techniques","Posts related with Anaerobic Culture Techniques.",{"slug":155,"name":327,"description":328,"image":42,"body":42,"postCount":186},"Immunoassays","You will get information about all the diagnostic tests that rely on the specific binding between an antigen and an antibody to detect or quantify a substance.",{"slug":330,"name":331,"description":332,"image":42,"body":42,"postCount":268},"biosafety-levels","Biosafety levels ","Articles related to Biosafety Levels",{"slug":334,"name":335,"description":336,"image":42,"body":42,"postCount":247},"environmental-factors","Environmental Factors ","In this case we are talking about growth requirements of microorganisms with deep dive in environmental factors that affect the growth. ",{"slug":338,"name":339,"description":340,"image":42,"body":42,"postCount":191},"pipette","Pipette","Posts related with Pipette. ",{"slug":342,"name":343,"description":344,"image":42,"body":42,"postCount":268},"bacteriology-mcqs","Bacteriology MCQs","This sections lists MCQs in Bacteriology.",{"slug":346,"name":347,"description":348,"image":42,"body":42,"postCount":349},"parasitology-mcqs","Parasitology MCQs","This section lists MCQs in Parasitology.",2,{"slug":351,"name":352,"description":353,"image":42,"body":42,"postCount":354},"virology-mcqs","Virology MCQs","This is the collections of Multiple Choice Questions in Virology.",4,{"slug":356,"name":357,"description":358,"image":42,"body":42,"postCount":247},"mcqs-in-microbiology","MCQs in Microbiology","This section lists the collections of Multiple Choice Questions in General Microbiology Topics. ",{"slug":360,"name":361,"description":362,"image":42,"body":42,"postCount":268},"immunology-mcqs","Immunology MCQs","In this section; we are posting collections of Multiple Choice Questions about Immunology. ",{"slug":364,"name":365,"description":366,"image":42,"body":42,"postCount":286},"microbial-curiosities","Microbial Curiosities","In this clusters, we are posting interesting and unique information about Microorganisms. ",{"slug":368,"name":369,"description":370,"image":42,"body":42,"postCount":371},"bacterial-culture-media","Bacterial Culture Media","Posts related to Bacterial Culture Media. ",23,{"slug":373,"name":374,"description":375,"image":42,"body":42,"postCount":191},"fungal-culture-media","Fungal Culture Media","Posts related to Fungal Culture Media.",{"slug":377,"name":378,"description":379,"image":42,"body":42,"postCount":247},"motility-test","Motility Test","This lists the procedure regarding various tests methods for bacterial motility.",{"slug":381,"name":382,"description":383,"image":42,"body":42,"postCount":286},"bacterial-enumeration","Bacterial enumeration","These posts are related to isolation and enumeration of bacteria. ",{"slug":385,"name":386,"description":387,"image":42,"body":42,"postCount":349},"gram-positive-coccobacillus","Gram-positive coccobacillus","List of Gram Positive Coccobacilli",{"slug":389,"name":390,"description":391,"image":42,"body":42,"postCount":354},"dimorphic-fungi","Dimorphic Fungi","This is about various dimorphic fungi. ",{"slug":393,"name":394,"description":395,"image":42,"body":42,"postCount":268},"bacterial-classification","Bacterial Classification","These posts are related with various approaches used for the classification of Bacteria. ",{"slug":397,"name":398,"description":399,"image":42,"body":42,"postCount":247},"immunofluorescence","Immunofluorescence ","Various Tests related to Immunofluorescence ",{"slug":401,"name":402,"description":403,"image":42,"body":42,"postCount":197},"antibody-mediated-immunity","Antibody-mediated Immunity","This clusters links the articles that are sharing insights about Antibody-mediated immunity. ",{"slug":405,"name":406,"description":407,"image":42,"body":42,"postCount":268},"hypersensitivity","Hypersensitivity","Articles related to Hypersensitivity.",{"slug":409,"name":410,"description":42,"image":42,"body":42,"postCount":411},"haemophilus","Haemophilus",3,{"slug":413,"name":414,"description":415,"image":42,"body":42,"postCount":354},"sexually-transmitted-infections-stis","Sexually transmitted infections (STIs)","This is the clusters of infections that are transmitted sexually. ",{"slug":417,"name":418,"description":419,"image":42,"body":42,"postCount":237},"adaptive-immunity","Adaptive Immunity","Blog posts related to B Cell Immunity and T Cell Immunity.",{"slug":421,"name":422,"description":423,"image":42,"body":42,"postCount":231},"fungal-diagnostics","Fungal Diagnostics","Various methods used for the Diagnosis of Fungal Infections. ",{"slug":425,"name":426,"description":427,"image":42,"body":42,"postCount":247},"laboratory-storage-and-preservation","Laboratory Storage and Preservation","Articles about Laboratory Storage of Antimicrobial Disk, Test organisms and Equipment used for this process. ",{"slug":429,"name":430,"description":431,"image":42,"body":432,"postCount":191},"laboratory-heating-equipment","Laboratory Heating Equipment","A guide to laboratory heating equipment, including hot plates, water baths, Bunsen burners, incubators, and dry baths, and how to choose the right one for each task.","Laboratory heating equipment covers the instruments that warm, melt, incubate, or sterilize samples and media in a microbiology laboratory. Each one delivers heat differently. \n\nA hot plate gives high, direct, dry heat; a water bath gives gentle, even, wet heat up to about 100°C; a Bunsen burner gives an open flame for rapid, very high heat; an incubator holds cultures at a steady temperature over hours or days; and a dry bath heats small tubes without water. Choosing the right one depends on the temperature you need, how precise it must be, and whether the sample can tolerate direct or open-flame heat.\n\nThe articles below cover each piece of heating equipment in detail, including its parts, working principle, uses, and the mistakes that most often go wrong at the bench.",{"slug":434,"name":435,"description":436,"image":42,"body":42,"postCount":197},"laboratory-glassware","Laboratory Glassware","Posts about Laboratory Glassware. ",{"slug":438,"name":439,"description":440,"image":42,"body":42,"postCount":197},"helminths","Helminths","In this section, we are covering properties, life cycle, pathogenesis and laboratory diagnosis of Helminths\u002FHelminthic infestations. ",{"slug":442,"name":443,"description":444,"image":42,"body":42,"postCount":252},"protozoan-parasite","Protozoan Parasite","In this cluster, we are covering protozoan parasites. ",{"slug":446,"name":447,"description":448,"image":42,"body":42,"postCount":202},"tests-for-gram-positive-cocci","Biochemical Tests for Gram Positive Cocci","This is the lists of Biochemical Tests that are used for Gram Positive Cocci. ",{"slug":450,"name":451,"description":452,"image":42,"body":42,"postCount":286},"bacterial-staining-technique","Bacterial Staining Technique","Lists of various staining techniques that are used to stain bacteria. ",{"slug":454,"name":455,"description":456,"image":42,"body":42,"postCount":277},"enzyme-tests","Enzyme Tests","\u003Cp>Various Biochemical Test that are based on enzymatic activity of the microorganisms. \u003C\u002Fp>",{"slug":458,"name":459,"description":460,"image":42,"body":42,"postCount":242},"carbohydrate-utilization","Carbohydrate Utilization","\u003Cp>Various biochemical tests which are related to Carbohydrate fermentation or Utilization\u003C\u002Fp>",{"slug":462,"name":463,"description":464,"image":42,"body":42,"postCount":247},"susceptibility-based-id","Susceptibility-based ID","\u003Cp>These are susceptibility based identification test such as optochin sensitivity, bacitracin sensitivity etc. \u003C\u002Fp>",{"slug":466,"name":467,"description":468,"image":42,"body":42,"postCount":354},"microbial-metabolism","Microbial Metabolism","\u003Cp>Tests about Microbial Metabolism. \u003C\u002Fp>",{"slug":470,"name":471,"description":472,"image":42,"body":42,"postCount":252},"substrate-utilization","Substrate Utilization","\u003Cp>The test in which a non-sugar carbon\u002Fnitrogen source is used or degraded (citrate, malonate, decarboxylases, indole, PAD).\u003C\u002Fp>",{"slug":474,"name":475,"description":476,"image":42,"body":42,"postCount":411},"atypical-pneumonia","Atypical Pneumonia","\u003Cp>Organisms responsible for Atypical Pneumonia. \u003C\u002Fp>",{"slug":478,"name":479,"description":480,"image":42,"body":42,"postCount":247},"antigen","Antigen","\u003Cp>Various articles related to Antigens.\u003C\u002Fp>",{"slug":482,"name":483,"description":484,"image":42,"body":42,"postCount":268},"innate-immunity","Innate Immunity","\u003Cp>Articles related to Innate Immunity. \u003C\u002Fp>",{"slug":486,"name":487,"description":488,"image":42,"body":42,"postCount":354},"respiratory-tract-infection","Respiratory Tract Infection","\u003Cp>In this cluster, you can see various etiological agents that causes respiratory tract infection. \u003C\u002Fp>",{"slug":490,"name":491,"description":492,"image":42,"body":42,"postCount":247},"torch-infection","TORCH Infection","\u003Cp>In this section; you can find articles related with TOCH infection. \u003C\u002Fp>",{"slug":494,"name":495,"description":496,"image":42,"body":42,"postCount":252},"microbiology-for-beginners","Microbiology for Beginners","\u003Cp>These articles are very basic articles, which will share general concepts in Microbiology. \u003C\u002Fp>",{"slug":498,"name":499,"description":500,"image":42,"body":42,"postCount":191},"dna-replication","DNA Replication","\u003Cp>Articles related to DNA and Replication of DNA. \u003C\u002Fp>",{"slug":502,"name":503,"description":504,"image":42,"body":42,"postCount":268},"genetic-code","Genetic Code","\u003Cp>Articles related to Genetic Code.\u003C\u002Fp>",{"slug":506,"name":507,"description":508,"image":42,"body":42,"postCount":268},"molecular-technique","Molecular Technique","\u003Cp>Posts related to Molecular Techniques. \u003C\u002Fp>",{"slug":510,"name":511,"description":42,"image":42,"body":42,"postCount":202},"colorimetric-assay","Colorimetric Assay ",{"slug":513,"name":514,"description":515,"image":42,"body":42,"postCount":247},"pharmaceutical-microbiology","Pharmaceutical Microbiology","\u003Cp>Various articles related to Pharmaceutical Microbiology\u003C\u002Fp>",{"slug":517,"name":518,"description":42,"image":42,"body":42,"postCount":411},"blood-and-immune-cells","Blood and Immune Cells",{"slug":520,"name":521,"description":42,"image":42,"body":42,"postCount":247},"host-pathogen-interaction","Host Pathogen Interaction",{"slug":523,"name":524,"description":42,"image":42,"body":42,"postCount":354},"blood-culture","Blood Culture",{"slug":526,"name":527,"description":42,"image":42,"body":42,"postCount":354},"environmental-microbiology","Environmental microbiology ",{"slug":529,"name":530,"description":42,"image":42,"body":42,"postCount":268},"copromicroscopic-technique","Copromicroscopic Technique",{"slug":532,"name":533,"description":42,"image":42,"body":42,"postCount":411},"quality-control","Quality Control",{"slug":535,"name":536,"description":42,"image":42,"body":42,"postCount":268},"dermatophytes","Dermatophytes",{"slug":538,"name":539,"description":42,"image":42,"body":42,"postCount":411},"viral-hemorrhagic-fevers","Viral Hemorrhagic Fevers",{"slug":541,"name":542,"description":42,"image":42,"body":42,"postCount":354},"h2s-production","H2S Production",{"slug":544,"name":545,"description":42,"image":42,"body":42,"postCount":349},"water-quality-testing","Water Quality Testing",{"slug":547,"name":548,"description":42,"image":42,"body":42,"postCount":247},"virology-basics","Virology basics",{"slug":550,"name":551,"description":42,"image":42,"body":42,"postCount":354},"typing-methods","Typing Methods",{"slug":553,"name":554,"description":42,"image":42,"body":42,"postCount":411},"blotting-technique","Blotting Technique",{"slug":556,"name":557,"description":42,"image":42,"body":42,"postCount":354},"history-microbiology","History of Microbiology"]