Use of the lymphocyte count as a diagnostic screen in adults with suspected Epstein-Barr virus infectious mononucleosis.

Objectives/hypothesis: To evaluate the predictive diagnostic accuracy of the lymphocyte count in Epstein-Barr virus-related infectious mononucleosis (IM).

Study Design: Retrospective case note and blood results review within a university-affiliated teaching hospital.

Methods: A retrospective review of 726 patients undergoing full blood count and Monospot testing was undertaken. Monospot testing outcomes were compared with the lymphocyte count, examining for significant statistical correlations.

Results: With a lymphocyte count of ≤4 × 10(9) /L, 99% of patients had an associated negative Monospot result (sensitivity of 84% and specificity of 94%). A group subanalysis of the population older than 18 years with a lymphocyte count ≤4 × 10(9) /L revealed that 100% were Monospot negative (sensitivity of 100% and specificity of 97%). A lymphocyte count of ≤4 × 10(9) /L correlated significantly with a negative Monospot result.

Conclusions: A lymphocyte count of ≤4 × 10(9) /L appears to be a highly reliable predictor of a negative Monospot result, particularly in the population aged >18 years. Pediatric patients, and adults with strongly suggestive symptoms and signs of IM, should still undergo Monospot testing. However, in adults with more subtle symptoms and signs, representing the vast majority, Monospot testing should be restricted to those with a lymphocyte count >4 × 10(9) /L.

Level Of Evidence: NA