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Infectious mononucleosis — ABIM Board MCQ

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HardInfectious DiseaseInfectious mononucleosisABIM Board

A 21-year-old has five days of fever, posterior cervical adenopathy, exudative pharyngitis and atypical lymphocytosis. A heterophile antibody test is negative. Which serologic pattern would best support acute primary EBV infection?

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Correct answer: C — Positive VCA IgM with absent EBNA antibody

The best answer is “Positive VCA IgM with absent EBNA antibody”. Heterophile testing can be negative early in infectious mononucleosis. Viral capsid antigen IgM appears early and disappears within weeks, whereas EBNA antibody is not present during acute primary infection and usually develops months later. VCA IgG plus EBNA without VCA IgM instead indicates remote infection.

Reference: CDC Laboratory Testing for Epstein-Barr Virus: https://www.cdc.gov/epstein-barr/php/laboratories/index.html