Challenging the use of the lymphocyte to white cell count ratio in the diagnosis of infectious mononucleosis by analysis of a large cohort of Monospot test results.

OBJECTIVE

We investigated the hypothesis that a lymphocyte/white cell count ratio should be used as a diagnostic indicator of infectious mononucleosis.

DESIGN

Retrospective study to compare lymphocyte counts and white blood cell counts, against the criterion standard, the mononucleosis spot test.

SETTING

Department of Otolaryngology, Mater Misericordiae University Hospital, Dublin, Ireland.

PARTICIPANTS

We reviewed 1000 patients who had Monospot assays, 500 positive and 500 negative.

MAIN OUTCOME MEASURES: The lymphocyte counts and white blood cell ratio was calculated and compared with the monospot result to calculate the sensitivity and specificity at various ratios.

RESULTS

The lymphocyte counts and white blood cell ratio was significantly different in the positive and negative monospot groups (P < 0.05). The mean lymphocyte counts and white blood cell ratio in the positive group was 0.49 and the mean lymphocyte to white cell count ratio in the monospot negative group was 0.29.A ratio of 0.35 had a specificity of 72% and a sensitivity of 84% for the detection of glandular fever. A higher ratio will give a greater specificity, but a lower sensitivity, and vice versa.

CONCLUSIONS

The mean lymphocyte to white cell count ratio is not sufficient to diagnose or exclude infectious mononucleosis. Thus, this study does not confirm the conclusions of earlier studies.