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Common blood test can help distinguish between mononucleosis and tonsillitis

January 16, 2007

Measuring a patient's ratio of white blood cell types may help physicians accurately distinguish between the similar conditions infectious mononucleosis and bacterial tonsillitis, potentially guiding treatment decisions, according to an article in the January issue of Archives of Otolaryngology-Head & Neck Surgery, one of the JAMA/Archives journals.

Acute tonsillitis (inflammation of the tonsils) and infectious mononucleosis (caused by the Epstein-Barr virus) are both common ear, nose and throat conditions with similar symptoms, according to background information in the article. These symptoms include sore throat, fever, painful swallowing, white plaque on the tonsils and redness of the throat and tonsils. "The importance in differentiating patients with tonsillitis from those with glandular fever [mononucleosis] is the prevention of spontaneous rupture of the spleen and acute intra-abdominal hemorrhage," potential complications of mononucleosis, the authors write. Currently, distinguishing between them requires an expensive mononucleosis spot test.

Dennis M. Wolf, B.Sc., D.O.-H.N.S., M.R.C.S., and colleagues at St. George's Hospital, London, retrospectively analyzed laboratory tests from 120 patients with infectious mononucleosis and 100 patients with bacterial tonsillitis treated at their facility. All patients were given the spot test for mononucleosis and additional blood tests were performed to determine the number of lymphocytes (a particular type of white blood cell involved in the body's immune response) and overall white blood cell count.

Total white blood cell count was significantly increased in the tonsillitis group compared with the mononucleosis group (16,560 cells per microliter vs. 11,400 cells per microliter), but the lymphocyte count was higher in the mononucleosis group (6,490 cells per microliter vs. 1,590 cells per microliter). The ratio of lymphocyte/white blood cell count ratio averaged .54 in the mononucleosis group and .10 in the tonsillitis group.

Based on this data, the researchers determined that a ratio higher than .35 would have a sensitivity of 90 percent and a specificity of 100 percent for the detection of mononucleosis, meaning that an individual with a ratio this high would be correctly diagnosed with mononucleosis 90 percent of the time and an individual with a ratio of .35 or lower would be correctly diagnosed as not having mononucleosis 100 percent of the time. "The specificity and sensitivity of this test seem to be better than the mononucleosis spot test itself," the authors write.

"In conclusion, we recommend that the lymphocyte-white blood cell count ratio should be used as an indicator to decide whether mononucleosis spot tests are required," they continue. "Results from our retrospective pilot study suggest that the lymphocyte-white blood cell count ratio could be a quickly available alternative test for the detection of glandular fever [mononucleosis]."

JAMA and Archives Journals