Monospot

1. Indications
   1. Infectious Mononucleosis suspected
2. Mechanism
   1. Test for heterophile Antibody (Paul-Bunnell IgM)
      1. Not specific to EBV
      2. Uncommonly occurs in other conditions
   2. Heterophil Antibody agglutinates Red Blood Cells
      1. Horse RBCs (most sensitive) - used for slide test
      2. Bovine RBCs
      3. Sheep RBCs (least sensitive)
3. Timing: Positive for Mononucleosis
   1. False negative Monospot common early in course
      1. Week 1: 25% false negative rate
      2. Week 2: 5-10% false negative rate
      3. Week 3: 5% false negative rate
   2. Positive Antibody tests
      1. Antibodies may appear within 1 week of symptom onset
      2. Monospot positive by week 3 in >90% of patients
      3. Antibodies peak between weeks 2 and 5
   3. Antibodies usually persist for 3 months
      1. Rarely antibodies persist up to 1 year
   4. Antibody development is age specific
      1. Age under 2 years: <30% develop antibodies
      2. Age 2-4 years: <75% develop antibodies
      3. Age <12 years: <50% develop antibodies
      4. Age >12 years: >70% develop antibodies
4. Interpretation: Positive Test (>1:40 titer)
   1. Infectious Mononucleosis (Epstein-Barr Virus)
      1. See Mononucleosis for approach to testing
   2. False positive causes (uncommon)
      1. Laboratory error (most common cause)
      2. CMV-Induced Mononucleosis
      3. Rubella
      4. Leukemia or Lymphoma
      5. Hepatitis
      6. Influenza
      7. Varicella Zoster Virus
      8. Systemic Lupus Erythematosus
      9. Malaria
      10. Pancreatic Cancer
5. References
   1. Gantz in Noble (2001) Primary Care, Mosby, p. 268
   2. Ravel (1995) Lab Medicine, Mosby-Year, p. 263-4