A young patient presents with fever, malaise and generalised lymphadenopathy, and has been evaluated for adenoid enlargement. Which test confirms the suspected diagnosis?

Correct answer: A. The heterophile antibody (Monospot) test for infectious mononucleosis

• A. CORRECT. Fever, malaise, pharyngitis and generalised LYMPHADENOPATHY in an adolescent or young adult is the classic picture of INFECTIOUS MONONUCLEOSIS caused by EPSTEIN–BARR VIRUS. The MONOSPOT test detects HETEROPHILE ANTIBODIES and confirms the diagnosis; supporting findings are atypical lymphocytosis on the blood film and, when the Monospot is negative early in the illness, EBV-specific serology (VCA IgM).
• B. The Mantoux test screens for tuberculosis exposure and is not indicated by this presentation.
• C. A rapid strep test identifies group A streptococcal pharyngitis. It is a reasonable differential, but streptococcal disease produces cervical lymphadenopathy rather than the GENERALISED lymphadenopathy and marked fatigue seen here.
• D. Rheumatoid factor assesses autoimmune arthritis and has no bearing on an acute infectious lymphadenopathy.

Note: Two points that matter clinically. First, SPLENOMEGALY occurs in roughly half of patients and carries a risk of splenic rupture — contact sport is prohibited for weeks. Second, giving AMPICILLIN or AMOXICILLIN to a patient with mononucleosis provokes a florid maculopapular rash in most patients; it is not true penicillin allergy but it is why the drug should be avoided when mononucleosis is suspected.