Contributed by Guest Blogger: L. Kantor ’14

Infectious mononucleosis was first brought about in 1889 with the expressed symptoms of pharyngitis, fever, and lymphadenopathy.  In 1920, it was discovered that many patients with “mono” had similar blood films, demonstrating an absolute lymphocytosis with abnormally abundant cytoplasm in mononuclear cells.  In 1932, the monospot test, a form of the heterophile antibody test, began being used to test for the disease.  Epstein-Barr virus, the currently identified cause of infectious mononucleosis, was identified in 1968.  The virus causes a high white blood cell count with a relative lymphocytosis, which is usually confirmed by a positive monospot test.  However, it has recently been suggested that a lymphocyte to white cell count (L/WCC) ratio could be a quickly available alternative test for the detection of infectious mononucleosis.  In a recent study, the L/WCC of a series of infected patients was compared with that of a similar number of patients with bacterial tonsillitis.  The researchers were trying to prove that a lymphocite/white cell count shows better specificity and sensitivity than the mononucleosis spot test.
One thousand monospot tests in patients with tonsillitis both in an outpatient and inpatient study were analyzed to compare L/WCC ratios in 500 positive and 500 negative results.  The lymphocyte counts and white blood cell ratio was significantly different in the positive and negative monospot groups.  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 detection of the Epstein-Barr virus.  However, these results show that a higher ratio will give a greater specificity, but a lower sensitivity, and vice versa.  Therefore, the mean lymphocyte to white cell count ratio is not sufficient to diagnose or exclude infectious mononucleosis.
However, some questions still arise.  Could the tests be equally accurate but simply at different stages of the infection?  Would the same results occur before the patient showed symptoms of infection?  Or after the symptoms disappeared?