Clinical inquiries. What test is the best for diagnosing infectious mononucleosis?

Tests for antibodies to Epstein-Barr viral capsid antigen or Epstein-Barr nuclear antigen are the most sensitive, are highly specific, and are also the most expensive for diagnosing infectious mononucleosis (strength of recommendation [SOR]: C, based on validating cohort study). Heterophile antibody tests have similar specificity and are cheaper, but are less sensitive in children or in adults during the early days of the illness (SOR: C, based on validating cohort study). The polymerase chain reaction assay for Epstein-Barr virus DNA is more sensitive than the heterophile antibody test in children, is highly specific, but is also expensive (SOR: C, based on validating cohort study). The percentages of atypical lymphocytes and total lymphocytes on a complete blood count provide another specific and moderately sensitive, yet inexpensive, test (SOR: C, based on validating cohort study).