[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$fRC9UM3T-aLcYYSWmuhyNRQPzboCobHLBEpzyfBgmq-o":32,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":47},[4,8,12,16,20,24,28],{"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},"Abbreviations","abbreviations","\u002Fabbreviations\u002F",{"title":25,"slug":26,"path":27},"Microbes","microbes","\u002Fmicrobes\u002F",{"title":29,"slug":30,"path":31},"Books","recommended-books","\u002Frecommended-books\u002F",{"type":33,"data":34},"blog",{"slug":35,"title":36,"description":36,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":39,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"body":43,"faq":44,"tags":45,"related":46},"fecal-occult-blood-test-principle-procedure-results","Fecal Occult Blood Test (FOBT): Procedure, Results",null,"Acharya Tankeshwar","2015-10-21","2026-06-30",false,"biochemical-tests","Bleeding into the gastrointestinal tract may be profuse with the vomiting of blood (haematemesis) or the passage of blood through the rectum (melaena). When the bleeding is chronic with only small amounts of blood being passed in the faeces, the blood (or its breakdown products) is not recognized in the faeces.\n\nThe fecal occult (hidden) blood test (FOBT) is a lab test used to check stool (feces) samples for hidden blood or blood products that may arise due to a small amount of bleeding in the gastrointestinal tract. Fecal occult blood is blood in feces that cannot be seen in the stool or on toilet paper by yourself.  Usually, we require approximately **200 cc** of blood to be able to visually recognize bleeding. Using FOBT we can detect bleeding that is **as little as 10 cc** of blood in the stool.\n\nOccult blood in the stool indicates gastro intestinal bleeding that may be because of helminth infestation (hookworm infection). Other conditions associated with internal gastro-intestinal bleeding are;\n\n- Oesophagitis (inflammation of the esophagus; often associated with acid reflux)\n- Esophageal cancer\n- Gastratitis\n- Stomach ulcer or cancer\n- Arterie venous malformation\n- Colon polyp\n- Colon cancer\n- Diverticulosis\n- Ulcerative colitis and\n- Hemorrhoid\n\n### Uses of Occult Blood Testing\n\nRequests for occult blood testing are usually made to investigate the cause of iron deficiency anemia or to assist in the diagnosis of bleeding lesions of the gastrointestinal tract, e.g. peptic ulcer, carcinoma, or diverticulosis.\n\n### Test Methods\n\n1. Chemically using laboratory reagents:  e.g. aminophenazone test.\n2. Immunologically using ready-made reagents in kit tests (more expensive and usually less stable than aminophenazone test)\n\n### Aminophenazone Test\n\nThis test detects the presence of hemoglobin in the test sample. Hemoglobin and its derivatives catalyze the transfer of oxygen from hydrogen peroxide to aminophenazone. Oxidation of aminophenazone produces a blue color (i.e. positive occult blood test)**.**\n\n### Reagents Required\n\n- Acetic acid 10% v\u002Fv\n- Alcohol, 95% v\u002Fv\n- Hydrogen peroxide 10 vols solution\n\n**Preparation of working Aminophenazone reagent**\n\nThe amounts given are sufficient for 1 test with positive and negative controls. Prepare fresh as follows:\n\n- Acetic acid 10% v\u002Fv: 1 ml\n- Alcohol, 95% v\u002Fv: 15 ml\n- 4 Aminophenazone (4-Aminoantipyrine):0.4g\n\nDissolve the aminophenazone in the alcohol solution and immediately before use add the acetic acid. Mix well.\n\n### Preparing for the test\n\n- Any source of blood will give a positive test. Blood from another source, like bleeding hemorrhoids or menstrual period, will interfere with the test.\n- **Do not eat red meat** before testing for the occult blood test. Red meat in the diet can give false-positive test results.\n- Do not eat cantaloupe,  fish, uncooked broccoli, turnip, radish, horseradish for 3 days before the test. Patient should eat plenty of vegetables, corn, and non-citrus fruits.  Any fruit juices containing ascorbic acid, iron, barium sulphate, cimetidine also has to be avoided 2\u002F3 days before testing.\n- Avoid drugs like aspirin, anti-inflammatory drugs, cough medicines for the 3 days before the test.\n- Taking vitamin C supplements may give false negative results. It is recommended not to take Vitamin C supplements for the 3 days before the test.\n\n### Procedure of Occult Blood Test (Chemical Method)\n\n1. Dispense about 7 ml of distilled water into a wide bore test tube.\n2. Add a sample of feces about 10-15 mm in diameter (taken from various parts of the specimen). Using a glass or plastic rod, emulsify the feces in the water.\n3. Allow the fecal particle to settle or centrifuge the emulsified specimen.\n4. Take three completely clean tubes and label them as;\n\nT: Patient’s Test\nNeg: Negative Control\nPos: Positive Control\n\n1. Add to each tube as follows:\n\nT: 5ml supernatant fluid from emulsified feces.\nNeg: 5 ml distilled water\nPos: 5 ml distilled water in which about 50 microliters of whole blood has been mixed\n\n1. Layer 5 ml of *working aminophenazone reagent* on top of the fluid in each tube (i.e. pipette down the side of each tube). *Do not mix.*\n2. Add 10 drops of the 10 vols hydrogen peroxide solution. Do not mix. Allow to stand for 1 minute.\n3. Look for the appearance of a blue color where the aminophenazone reagent meets the sample or control solutions.\n\n### Report the test results\n\n1. No color Change: Negative test\n2. Pale Blue: Positive +\n3. Dark blue: Positive + +\n4. Blue-black: Positive + + +\n\n**Control**\n\n- Negative Control: This should show no color change.\n- Positive Control: This should show a positive reaction.\n\n### Interpretation of Results and Sources of Errors\n\n**A positive result** means that the test has detected blood. This does not mean you have tested positive for cancer or any other illness. It is just an indication of internal bleeding which will require a formal evaluation of the patient’s gastrointestinal tract. Physician may request colonoscopy or endoscopy to examine the entire lining of the gastrointestinal tract. The commonest causes of positive occult blood tests in tropical and other developing countries are **hookworm infection**, peptic ulcer any other causes mentioned above.\n\n**False Positive** result: A false positive reaction may occur if the faeces contains peroxidase-like substances. Such reactions may be avoided by dietary restrictions (read above-preparing for the test). Further testing and examinations should be performed by the physician to determine the exact cause and source of the occult blood in the stool.\n\nA **false negative** reaction may be obtained if the faeces contains  a high concentration of ascorbic acid.\n\n**Note:** If the test is negative but there is high clinical suspicion, two further specimens should be tested to detect bleeding which may be intermittent.\n\n**References**\n\n1. Kaur K, Zubair M, Adamski JJ. Fecal Occult Blood Test. [Updated 2023 Apr 23]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: [https:\u002F\u002Fwww.ncbi.nlm.nih.gov\u002Fbooks\u002FNBK537138\u002F](https:\u002F\u002Fwww.ncbi.nlm.nih.gov\u002Fbooks\u002FNBK537138\u002F)\n2. Narula, N., Ulic, D., Al-Dabbagh, R., Ibrahim, A., Mansour, M., Balion, C., & Marshall, J. K. (2014). Fecal occult blood testing as a diagnostic test in symptomatic patients is not useful: a retrospective chart review. *Canadian journal of gastroenterology & hepatology*, *28*(8), 421–426. [https:\u002F\u002Fdoi.org\u002F10.1155\u002F2014\u002F189652](https:\u002F\u002Fdoi.org\u002F10.1155\u002F2014\u002F189652)",[],[],[],[48,54,61,66,70,74,79,84,88,92],{"slug":49,"name":38,"description":50,"image":51,"body":52,"postCount":53},"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.*",433,{"slug":55,"name":56,"description":57,"image":58,"body":59,"postCount":60},"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.",81,{"slug":62,"name":63,"description":64,"image":37,"body":37,"postCount":65},"sushmita-baniya","Sushmita Baniya","Author \u002F Contributor",32,{"slug":67,"name":68,"description":64,"image":37,"body":37,"postCount":69},"samikshya-acharya","Samikshya Acharya",20,{"slug":71,"name":72,"description":64,"image":37,"body":37,"postCount":73},"alisha-tripathi","Alisha Tripathi",6,{"slug":75,"name":76,"description":77,"image":37,"body":37,"postCount":78},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor",9,{"slug":80,"name":81,"description":82,"image":37,"body":37,"postCount":83},"guest-author","Guest Author","Guest Author \u002F Contributor",2,{"slug":85,"name":86,"description":64,"image":37,"body":37,"postCount":87},"srijana-khanal","Srijana Khanal",18,{"slug":89,"name":90,"description":82,"image":37,"body":37,"postCount":91},"dr-poonam-acharya","Dr. Poonam Acharya",1,{"slug":93,"name":94,"description":64,"image":37,"body":95,"postCount":96},"nisha-rijal","Nisha Rijal","**Nisha Rijal** is a microbiologist and quality assurance specialist. She served for nearly 12 years as a microbiologist at the National Public Health Laboratory (NPHL), Nepal's national reference laboratory, and continues to work as a consultant microbiologist in international public health organization. ",51]