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 Laryngoscope , 123:2401–2404, 2013