From the Guidelines
To rule out infectious mononucleosis (mono) in a patient with month-long fatigue following a viral illness, I recommend ordering EBV-specific antibody testing, including VCA-IgM, VCA-IgG, and EBNA-IgG antibodies, as the initial step. This approach is based on the guidelines provided by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM) 1. The presence of VCA IgM (with or without VCA IgG) antibodies in the absence of antibodies to EBNA indicates recent primary infection with EBV, which is consistent with the patient's symptoms.
The Monospot test, which detects heterophile antibodies, can be used as an initial screening tool but may not be as sensitive, especially in the first week of illness or in children, and can also yield false-positive results in certain conditions such as leukemia, pancreatic carcinoma, viral hepatitis, or CMV infection 1. Given that the patient has had symptoms for a month, the EBV-specific antibody testing is more appropriate for determining the stage of infection.
Key points to consider in the interpretation of these tests include:
- The presence of VCA IgM antibodies indicates recent infection.
- The presence of EBNA antibodies suggests infection occurred more than 6 weeks prior to testing.
- Over 90% of the adult population has IgG class antibodies to VCA and EBNA antigens, indicating past infection.
- Approximately 5%–10% of patients who have been infected with EBV fail to develop antibodies to the EBNA antigen.
If the results of the EBV-specific antibody testing do not support a diagnosis of acute EBV infection, and clinical suspicion for mono or another infectious cause of prolonged fatigue remains high, further testing for other pathogens such as CMV, toxoplasmosis, or HIV may be warranted 1. The goal of testing is to identify the cause of the patient's symptoms to guide management and provide prognostic information regarding recovery time. Treatment for EBV infection is generally supportive, focusing on rest, hydration, and management of symptoms while the infection resolves.
From the Research
Diagnostic Tests for Infectious Mononucleosis
To rule out mono in a patient with fatigue for a month since a viral illness, the following tests can be considered:
- Heterophile antibody tests, such as the Monospot test, which detect antired cell antibodies produced during EBV infection 2, 3, 4
- Serologic testing for antibodies to viral capsid antigens, which is recommended when confirmation of the diagnosis is required in patients with a negative mono-spot test 2
- Polymerase chain reaction assay for Epstein-Barr virus DNA, which is more sensitive than the heterophile antibody test in children, but also expensive 3
- Complete blood count, which provides another specific and moderately sensitive test, and is inexpensive 3
Test Characteristics
The characteristics of these tests are:
- Heterophile antibody tests: rapid, cheap, and specific, but have low sensitivity and low negative predictive value in young children 4
- Serologic testing: allows diagnosis and staging of EBV infection, but has cross-reaction with other herpesvirus infections, a longer turnaround time, and is more expensive 4
- Polymerase chain reaction assay: highly sensitive and specific, but expensive 3
- Complete blood count: moderately sensitive and specific, and inexpensive 3
Test Selection
The selection of the test depends on the patient's age, clinical presentation, and the need for confirmation of the diagnosis. In adolescents, heterophile antibody tests have high specificity and sensitivity, but in young children, virus-specific serology may be required 4. If the mono-spot test is negative, serologic testing for antibodies to viral capsid antigens is recommended 2.