What is the comparison between monospot (Mononucleosis Spot Test) and EBV (Epstein-Barr Virus) antibody profile for diagnosing infectious mononucleosis?

Monospot vs. EBV Antibody Profile for Mononucleosis Diagnosis

The EBV antibody profile is superior to monospot testing for diagnosing infectious mononucleosis, particularly in children under 10 years and during the first week of illness when false-negative monospot results are common. 1

Diagnostic Test Characteristics

Monospot (Heterophile Antibody) Test

• Sensitivity and Specificity: 87% sensitivity and 91% specificity 2
• Timing: Heterophile antibodies typically become detectable between days 6-10 after symptom onset 1
• Limitations:
  • False-negative results occur in approximately 10% of patients 1
  • Particularly unreliable in children younger than 10 years 1, 2
  • Often negative during the first week of illness 2, 3
  • May remain positive for a year or longer after infection 1
• False-positives: Can occur in patients with leukemia, pancreatic carcinoma, viral hepatitis, and CMV infection 1

EBV Antibody Profile

• Components: Tests for IgG and IgM to viral capsid antigen (VCA) and antibodies to Epstein-Barr nuclear antigen (EBNA) 1
• Interpretation:
  • Acute primary infection: VCA IgM positive (with or without VCA IgG) and EBNA antibodies negative 1, 4
  • Past infection: VCA IgG and EBNA antibodies positive, VCA IgM negative 1
• Advantages: More sensitive and specific than heterophile antibody testing 2
• Limitations: More expensive and takes longer to process than rapid heterophile testing 2

Diagnostic Algorithm

1. Initial Testing:

   • Complete blood count with differential (looking for >40% lymphocytes and >10% atypical lymphocytes) 2
   • Monospot (heterophile antibody) test 1, 2

2. If Monospot Positive:

   • Diagnosis of infectious mononucleosis confirmed
   • No further testing needed in typical cases 4

3. If Monospot Negative but Clinical Suspicion Remains:

   • Consider EBV-specific antibody testing, especially in:
     • Children under 10 years 1
     • First week of illness 2, 3
     • Atypical or severe presentations 4
     • Immunocompromised patients 1

4. EBV Antibody Profile Interpretation:

   • VCA IgM+, VCA IgG+/-, EBNA- = Acute EBV infection 1, 4
   • VCA IgM-, VCA IgG+, EBNA+ = Past EBV infection 1
   • VCA IgM-, VCA IgG-, EBNA- = No EBV infection 4

5. If Both Tests Negative but Mononucleosis-Like Illness Persists:

   • Consider alternative diagnoses such as CMV, adenovirus, HIV, HHV-6, HSV, Streptococcus pyogenes, or Toxoplasma gondii 3

Clinical Considerations

• The EBV antibody profile is particularly valuable when:

  • Evaluating patients with negative monospot tests but classic symptoms 1
  • Differentiating between acute and past infection 1
  • Assessing immunocompromised patients who may develop EBV-associated lymphoproliferative disease 1

• Liver enzyme testing can increase clinical suspicion for infectious mononucleosis when heterophile antibody testing is negative 2

Pitfalls to Avoid

• Relying solely on monospot testing in children under 10 years, as false-negatives are common 1
• Assuming a negative monospot test early in the course of illness rules out EBV infection 2, 3
• Failing to consider alternative diagnoses that can mimic infectious mononucleosis when both monospot and EBV antibody tests are negative 3
• Using suboptimal tests like the Paul-Bunnell test instead of more modern assays 1
• Misinterpreting persistent VCA IgG and EBNA antibodies, which remain positive for life after infection and do not indicate acute disease 1