Quick Test Can Distinguish Tonsillitis from Mononucleosis

LONDON, Jan. 15 -- As a rapid screening tool, the ratio of a patient's white blood cell types differentiated acute purulent tonsillitis from infectious mononucleosis, researchers here reported.

A ratio of lymphocyte to white blood cell count (L/WCC) higher than 0.35 indicated that the patient would be correctly diagnosed as having mononucleosis 100% of the time, according to a retrospective pilot study in the January issue of the Archives of Otolaryngology Head and Neck Surgery.

The test could help determine whether mononucleosis spot tests are required, said Dennis Wolf, B.Sc., D.O.-H.N.S., of St. George's Hospital here, and colleagues. This would prevent unnecessary requests for the slower expensive mononucleosis spot tests and facilitate the use of appropriate treatment and possibly shorter hospital stays,

The findings came from a retrospective analysis of 120 patients with infectious mononucleosis and 100 patients with bacterial tonsillitis treated at St. George's Hospital. All patients were given the mononucleosis spot test, as well as a lymphocyte and overall white blood cell count, from which the L/WCC ratio was calculated.

The distribution of male and female patients was similar in the two groups, although the mononucleosis patients were somewhat younger (mean age 23.08 years) than the tonsillitis patients (mean 27 years), which was expected considering the known epidemiological data, the researchers said.

Significant differences were evaluated using the Mann-Whitney test and Fisher exact test.

Analyzing the data, the researchers found that the mean (SD) total white blood cell count was significantly higher (P<.001) in the tonsillitis group (16, 560/?L [541/?L] ) compared with (11,400/?L [4,670/?L] ) in the mononucleosis group.

However, the lymphocyte count was significantly higher (P<.001) in the mononucleosis group (6,490/?L [3,590/?L]) compared with the tonsillitis group (1,590/?L [680/?L]).

In addition to these findings, the neutrophil count was increased (P<.001) in the tonsillitis group (13, 770/?L) compared with the mononucleosis group (3,830/?L).

The mean lymphocyte/ white blood cell ratio was significantly different in the two groups (P<.001), the researchers said. The mean L/WCC ratio in the mononucleosis group was 0.54 (0.14) compared with 0.10 (0.08) in the bacterial tonsillitis group.

The researchers then calculated that a ratio higher than 0.35 had a specificity of 100% and a sensitivity of 90% for the detection of mononucleosis. Thus an individual with a ratio this high would be correctly diagnosed as having mononucleosis 90% of the time, while a person with a ratio of 0.35 or lower would be correctly diagnosed as not having mononucleosis 100% of the time.

The data suggest that the specificity and sensitivity of this test seem to be better that the mononucleosis spot test itself, the researchers said.

The expensive mononucleosis spot test at St. George's Hospital can take up to 48 hours after admission for the results to become available. This produces additional costs for the hospital and risks for the patients, Dr.Wolf said.

In addition, the researchers wrote, the spot test can produce false-negative results, and the test's true sensitivity should be determined by Epstein-Barr-specific serologic tests.

The importance of differentiating patients with tonsillitis from those with mononucleosis is the prevention of spontaneous rupture of the spleen, though rare, and acute intra-abdominal hemorrhage. Patients with mononucleosis should also have further follow-up with liver-function rests, they said.

"Further prospective studies, including Epstein Barr serologic tests, may determine the exact sensitivity and specificity of our easily available test," the researchers said.

However, they said, "we recommend that the L/WCC ratio should be used as an indicator to decide whether mononucleosis spot tests are required."

Results from this retrospective pilot study, Dr. Wolf said, suggest that the lymphocyte/ white blood cell count ratio could be used as a quickly available alternative test for the detection of mononucleosis.