What is a Monospot Test?
The Monospot test is a rapid screening blood test that detects heterophile antibodies to diagnose infectious mononucleosis caused by Epstein-Barr virus (EBV). 1
Test Mechanism and Specimen Requirements
- The test detects heterophile antibodies that develop during EBV infection, making it a useful first-line diagnostic tool 2
- The optimal specimen is serum collected in a clot tube at room temperature, with transport to the laboratory within 2 hours 1
- The test is also referred to as the heterophile antibody test in clinical practice 1, 3
Diagnostic Performance
Sensitivity and Specificity
- The test demonstrates sensitivity of 70-92% and specificity of 96-100% for EBV-associated infectious mononucleosis 4
- A positive Monospot test may be considered diagnostic for EBV infection and no further EBV-specific testing is required 1, 2
False Negative Results
- Up to 10% of Monospot tests yield false negative results, occurring most commonly in younger children 1, 2, 5
- Heterophile antibodies may take time to develop early in infection, potentially requiring repeat testing 2
- When clinical suspicion remains high despite a negative test, EBV-specific serologic testing (IgG and IgM to viral capsid antigen, and antibodies to Epstein-Barr nuclear antigen) should be performed on the same sample 1, 2
- Alternatively, the Monospot can be repeated on a serum specimen obtained 7-10 days later, at which time it is more likely to be positive if the patient has EBV infection 1
False Positive Results
- False positives may occur in patients with leukemia, pancreatic carcinoma, viral hepatitis, CMV infection, systemic lupus erythematosus, and rubella 2, 4
- Rare cross-reactivity has been reported with dengue fever 4
- Isolated false-positive results can persist for years without clinical significance 6
Clinical Algorithm for Use
When Monospot is positive: Consider the diagnosis confirmed; no additional EBV testing needed 1, 2
When Monospot is negative but clinical suspicion is high:
- Perform EBV-specific serologic testing immediately using the same sample 1, 2
- Test for VCA IgM, VCA IgG, and EBNA antibodies 1, 2
- Recent primary infection shows VCA IgM positive (with or without VCA IgG) and EBNA negative 2
Critical Pitfalls to Avoid
- Do not rely solely on a negative Monospot to rule out infectious mononucleosis, especially in children under 10 years of age 1, 2
- Failing to order EBV-specific serology when clinical suspicion remains high can delay diagnosis 2, 5
- The Paul-Bunnell and Monospot tests are considered suboptimal compared to EBV-specific serologic testing in certain populations 1