From the Guidelines
The best test for infectious mononucleosis is the Monospot test, also known as the heterophile antibody test, due to its rapid results and wide availability, although EBV-specific antibody tests, such as those for viral capsid antigen (VCA) IgM and IgG, are recommended for more definitive diagnosis, especially in cases with negative Monospot results but strong clinical suspicion 1.
Key Points to Consider
- The Monospot test detects heterophile antibodies produced by the immune system in response to Epstein-Barr virus (EBV) infection, which causes most cases of mononucleosis.
- The test provides results within minutes and is widely available in outpatient settings, but has limitations, particularly in children under 4 years old and during the first week of illness, when false negatives are common 1.
- For more definitive diagnosis, especially in cases with negative Monospot results but strong clinical suspicion, EBV-specific antibody tests are recommended, including tests for VCA IgM and IgG, early antigen (EA), and Epstein-Barr nuclear antigen (EBNA) antibodies 1.
- The presence of VCA IgM antibodies indicates acute infection, while the pattern of other antibodies helps distinguish between recent and past infections.
- These specific serologic tests are more sensitive and specific than the Monospot test but take longer to process and are more expensive.
Diagnostic Approach
- Primary EBV infection is diagnosed by the detection of IgM and IgG directed against the EBV viral capsid antigen (VCA) with negative EBNA1 IgG 1.
- Biopsy diagnosis and classification by a specialist haematopathologist is required to differentiate infectious mononucleosis from lymphoproliferative disease, non-Hodgkin's lymphoma, and Hodgkin's disease, with analysis including EBER in situ hybridisation to detect the presence of EBV 1.
From the Research
Diagnostic Tests for Infectious Mononucleosis
The diagnosis of infectious mononucleosis can be made using various tests, including:
- Heterophile antibody tests, such as the monospot test 2
- Serologic tests for antibodies to Epstein-Barr virus (EBV) viral capsid antigen (VCA) and Epstein-Barr nuclear antigen (EBNA) 3, 2, 4
- Plasma EBV-DNA test 5
- Peripheral blood routine test, including lymphocytosis 5
- Polymerase chain reaction assay for EBV DNA 4
Sensitivity and Specificity of Diagnostic Tests
The sensitivity and specificity of these tests vary, with:
- Heterophile antibody tests having similar specificity but lower sensitivity in children or in adults during the early days of the illness 4
- Serologic tests for antibodies to EBV VCA and EBNA being the most sensitive and highly specific, but also the most expensive 4
- Plasma EBV-DNA test having a higher diagnostic value than the VCA-IgG avidity test in children aged <6 years, especially aged <3 years 5
- Peripheral blood routine test, including lymphocytosis, being suitable for the early stage of the disease 5
Recommendations for Diagnostic Testing
Based on the available evidence, the following tests are recommended for diagnosing infectious mononucleosis:
- Monospot test or other heterophile antibody tests as the initial test 2
- Serologic tests for antibodies to EBV VCA and EBNA in cases where the heterophile antibody test is negative 3, 2, 4
- Plasma EBV-DNA test or polymerase chain reaction assay for EBV DNA in children or in cases where the diagnosis is uncertain 5, 4