From the Guidelines
The best way to confirm a diagnosis of infectious mononucleosis in a 3-year-old patient with a 7-day history of symptoms is through Epstein-Barr virus (EBV) specific serology, particularly viral capsid antigen (VCA) IgM and IgG, and Epstein-Barr nuclear antigen (EBNA) antibodies, as heterophile antibody tests may have limited sensitivity in young children 1. When diagnosing infectious mononucleosis, it's crucial to consider the patient's age and the timing of the symptoms. In this case, the patient is 3 years old and has had symptoms for 7 days.
- The heterophile antibody test, also known as the Monospot test, may not be reliable in children under 4 years of age, with false negatives occurring in up to 10% of cases, and especially common in children younger than 10 years 1.
- A complete blood cell count (CBC) with differential may show an elevated white blood cell count with an increased percentage of atypical lymphocytes, which is common in EBV-associated mononucleosis, but this is not specific enough for a definitive diagnosis 1.
- Peripheral blood smear may also show atypical lymphocytes, but this is also not specific enough for a definitive diagnosis.
- EBV-specific antibody testing, including VCA IgM and IgG, and EBNA antibodies, is the most reliable method for confirming a diagnosis of infectious mononucleosis in a 3-year-old patient, as it can indicate recent primary infection with EBV 1. Key points to consider when interpreting the results of EBV-specific antibody testing include:
- The presence of VCA IgM antibodies indicates acute infection.
- The absence of EBNA antibodies in the presence of VCA IgM strongly supports recent infection.
- The presence of EBNA antibodies indicates infection more than 6 weeks from the time of the sample and therefore not likely implicating EBV as a cause 1.
From the Research
Diagnostic Approaches for Infectious Mononucleosis
To confirm a diagnosis of infectious mononucleosis in a 3-year-old patient with a 7-day history of symptoms, several diagnostic approaches can be considered:
- Complete blood cell count with differential: This test can help assess for lymphocytosis and the presence of atypical lymphocytes, which are common in infectious mononucleosis 2.
- Heterophile antibody testing: Although this test has a sensitivity of 87% and specificity of 91%, it may have a false-negative result in children younger than five years and in adults during the first week of illness 2.
- Immunoglobulin viral capsid antigen testing: This test is more sensitive and specific than heterophile antibody testing but is also more expensive and takes longer to process 2.
- Peripheral blood smear: This test can help identify atypical lymphocytes, which are characteristic of infectious mononucleosis.
Considerations for Young Children
In young children, especially those under 3 years old, the plasma EBV-DNA test has a higher diagnostic value than the VCA-IgG avidity test 3. Additionally, EBV antibody detection should be combined with EBV nucleic acid detection in children under 6 years old and in the early stage of the disease 3.
Choosing the Best Diagnostic Approach
Given the age of the patient and the duration of symptoms, the best diagnostic approach may involve a combination of tests, including complete blood cell count with differential, immunoglobulin viral capsid antigen testing, and possibly plasma EBV-DNA testing 3, 2. Heterophile antibody testing may not be the most reliable option in this case due to the patient's age and the potential for false-negative results 2.