Positive Monospot Test: Diagnosis and Management
A positive Monospot test in a young adult with fever, sore throat, and fatigue confirms infectious mononucleosis (IM), and management is entirely supportive with activity restriction for 8 weeks to prevent splenic rupture. 1, 2
Confirming the Diagnosis
When the Monospot is positive:
- The rapid heterophile antibody (Monospot) test becomes positive between days 6-10 after symptom onset and has 71-90% accuracy for diagnosing IM 1, 3
- A positive test in the appropriate clinical context (fever, pharyngitis, lymphadenopathy, fatigue) is sufficient to confirm the diagnosis 1, 4
- No additional serologic testing is needed when the Monospot is positive and clinical features are consistent 1
If confirmation is needed despite a positive Monospot:
- Check EBV-specific antibodies: VCA IgM (with or without VCA IgG) in the absence of EBNA antibodies confirms recent primary EBV infection 1
- EBNA antibodies develop 1-2 months after primary infection; their presence indicates infection occurred more than 6 weeks prior and makes acute mononucleosis unlikely 1
Expected Laboratory Findings
- Peripheral blood leukocytosis with lymphocytes comprising at least 50% of the white blood cell differential 2
- Atypical lymphocytes constituting more than 10% of the total lymphocyte count 2, 4
- Elevated serum transaminases are common 2, 5
- IM is unlikely if the lymphocyte count is less than 4,000/mm³ 3
Treatment Approach
Supportive care only:
- Treatment is entirely supportive; aciclovir does not ameliorate the course of IM in otherwise healthy individuals 1
- Reduction of activity and bed rest as tolerated are recommended 2
- Symptomatic relief with antipyretics (acetaminophen or ibuprofen) for fever and pain 3
Corticosteroids:
- Reserve corticosteroids only for airway obstruction or severe pharyngeal edema causing respiratory compromise 1
- Glucocorticoids do not reduce the length or severity of illness in uncomplicated cases 3
Critical Activity Restrictions
Preventing splenic rupture:
- Patients must avoid contact sports or strenuous exercise for 8 weeks or while splenomegaly is still present 2
- Spontaneous splenic rupture occurs in 0.1-0.5% of patients and is potentially life-threatening 2, 4
- Physical activity within the first three weeks of illness may increase the risk of splenic rupture 3
Expected Clinical Course
- Fatigue may be profound but tends to resolve within three months 2
- Splenomegaly occurs in approximately 50% of cases and hepatomegaly in 10% 2
- Periorbital and/or palpebral edema, typically bilateral, occurs in one-third of patients 2
- A maculopapular rash occurs in approximately 10-45% of cases 2
- Most patients have an uneventful recovery 2
Complications to Monitor
Immediate concerns:
- Airway obstruction is the most common cause of hospitalization, particularly in children 3
- Splenic rupture is the most feared complication 2, 4
Long-term sequelae:
- Infectious mononucleosis is a risk factor for chronic fatigue syndrome 2
Special Populations
Immunocompromised patients:
- Have increased risk of EBV-associated lymphoproliferative disease and require specialist consultation 1
- If on immunomodulator therapy, obtain full blood count, blood film, and liver function tests 1
- Immunomodulator therapy should be reduced or discontinued if possible 1
- Patients with immunosuppression are more likely to have fulminant EBV infection 3
Common Pitfalls to Avoid
- Do not prescribe antibiotics unless bacterial superinfection is documented; ampicillin/amoxicillin causes a rash in 80-100% of IM patients 2
- Do not allow return to sports or strenuous activity before 8 weeks, even if the patient feels better 2
- Do not use antivirals routinely; they provide no benefit in immunocompetent patients 1, 3