What are the recommended tests for diagnosing mononucleosis?

Recommended Testing for Mononucleosis

The recommended initial diagnostic testing for mononucleosis includes a complete blood count (CBC) with differential to assess for lymphocytosis with atypical lymphocytes, followed by a rapid heterophile antibody test (Monospot). 1

Initial Diagnostic Approach

• A CBC with differential is recommended as the first-line test, looking specifically for:

  • Lymphocytosis (>40% lymphocytes) 1
  • Atypical lymphocytes (>10% of total lymphocyte count) 2
  • Leukocytosis, which is more common in EBV-positive cases 3

• Heterophile antibody testing (Monospot test) should be performed as the initial serologic test due to its:

  • Rapid results availability 1
  • Good sensitivity (87%) and specificity (91%) in adolescents and adults 1
  • Wide availability and cost-effectiveness 1

When to Pursue Additional Testing

• If the heterophile antibody test is negative but clinical suspicion remains high, consider:

  • Liver function tests (elevated liver enzymes increase clinical suspicion for mononucleosis) 1
  • EBV-specific antibody testing 4

• EBV-specific serologic testing is indicated in the following scenarios:

  • Patients with negative heterophile antibody tests but persistent clinical suspicion 4
  • Children younger than 10 years (who commonly have false-negative heterophile tests) 4
  • Patients in the first week of illness (when heterophile antibodies may not yet be detectable) 1
  • Atypical or severe presentations requiring confirmation 5

EBV-Specific Antibody Testing

When EBV-specific antibody testing is needed, the recommended panel includes:

• Viral Capsid Antigen (VCA) antibodies:

  • IgM antibodies to VCA - present in acute infection 4, 5
  • IgG antibodies to VCA - may be present in acute infection and persist indefinitely 5

• Epstein-Barr Nuclear Antigen (EBNA) antibodies:

  • Typically absent in acute infection 4
  • Develop 1-2 months after primary infection and remain detectable for life 4

• Early Antigen (EA) antibodies:

  • May provide additional confirmation in some cases 5

Interpretation of EBV-Specific Antibody Results

• Acute primary EBV infection is indicated by:

  • Presence of VCA IgM (with or without VCA IgG) 4
  • Absence of EBNA antibodies 4, 5

• Past infection (not acute) is indicated by:

  • Presence of VCA IgG and EBNA antibodies 4
  • Absence of VCA IgM 5

Special Considerations

• For patients with negative heterophile tests but mononucleosis-like symptoms, consider testing for other causes:

  • Cytomegalovirus (CMV) 4
  • Adenovirus 4
  • HIV 4
  • Toxoplasma gondii 4

• In immunocompromised patients, consider more extensive testing due to higher risk of severe disease:

  • EBV viral load by nucleic acid amplification testing (NAAT) may be useful 4
  • Testing for EBV-associated lymphoproliferative disease may be indicated 4

Common Pitfalls to Avoid

• False-negative heterophile antibody results commonly occur in:

  • Children under 10 years of age (approximately 10% of all patients) 4
  • Early disease (first week of symptoms) 1

• False-positive heterophile antibody results may occur in:

  • Leukemia 4
  • Pancreatic carcinoma 4
  • Viral hepatitis 4
  • CMV infection 4

• Relying solely on clinical presentation without laboratory confirmation can lead to misdiagnosis, as other conditions can mimic infectious mononucleosis 2, 6