Monospot test: Principle, Procedure, Uses

Last updated on June 2nd, 2021

Monospot test is a form of the heterophile antibody test which is used for the rapid screening of infectious mononucleosis (mono).  Epstein–Barr virus (EBV) causes the disease infectious mononucleosis. Blood, serum, or plasma is taken and is looked for the presence of heterophil antibodies.

When a person is infected with Epstein-Barr virus (EBV), the immune system makes antibodies to fight this infection which is detected in the blood using this test. Monospot testing can usually detect antibodies 2 to 9 weeks after a person is infected.

Paul and Bunnell were the first scientists which suggested the use of hemagglutination of sheep RBC as a method of detecting heterophile antibodies associated with infectious mononucleosis.

Sample:

Serum/Plasma: Serum or plasma may be used with the monospot test, provided whole blood is collected by an acceptable medical technique. Avoid using grossly hemolyzed sera. Serum should be clear and free of bacterial contamination. Specimens can be stored at 2 to 8°C for 24 h. For prolonged storage, specimens should be frozen (-20°C).

Principle: 

A sample of the patient’s serum/plasma is placed on a microscope slide and mixed with guinea pig kidney antigen and preserved horse erythrocytes (these reagents can be purchased from commercial suppliers of kits). Throughly mixed the reagents and rock the slide for a minute.  If heterophil antibodies are present in the serum/plasma, the blood clumps (agglutinates). This result usually indicates a mono infection. It typically is not used to diagnose mono that started more than 6 months earlier. The results of a monospot test are usually ready within 1 hour.

Heterophile-antibody test

Results:

  1. Normal (negative): The blood sample does not form clumps (no heterophil antibodies are detected).
  2. Abnormal (positive): The blood sample clumps (heterophil antibodies are detected). If the blood sample clumps, you probably have mono.

Accuracy of Monospot Test

Studies have shown that monospot test produces both false-positive and false-negative results. Results should be correlated with clinical and hematological findings.

1. False Positive Reactions: The antibodies detected by monospot can be caused by conditions other than infectious mononucleosis. It may occur in persons with:

  1. Leukemia or lymphoma
  2. Hepatitis
  3. Rubella
  4. Systemic lupus erythematosus (SLE)
  5. Toxoplasmosis


2.  False Negative Reactions:

  • Children, especially those younger than 2 years, are more likely than adults to have a negative monospot test (25%–50%), even when they have infectious mononucleosis.
  • It takes time to develop antibodies if the test is done within the first few weeks of becoming infected with EBV (approx. 25% false-negative rate in first week). This may lead to a false-negative result.
  • If the first test does not indicate mono but you still have symptoms, the test may be repeated.

Uses of Monospot Test:

The monospot test is not recommended for general use. Monospot test may indicate that a person has a typical case of infectious mononucleosis, but does not confirm the presence of EBV infection.

References and further readings

  1. Marshall-Andon T, Heinz P. How to use … the Monospot and other heterophile antibody tests. Archives of Disease in Childhood – Education and Practice 2017;102:188-193.
About Acharya Tankeshwar 474 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.

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