[Importance of machine blood count in the diagnosis of infectious mononucleosis by EBV]

EBV serology is recommended for serological diagnosis of mononucleosis. As results of an automated differential blood count is available more quickly, possible differences between an EBV primary infection and a bacterial tonsillitis were investigated.

A retrospective evaluation of absolute and relative lymphocyte and monocyte counts of n = 140 patients > 16 years from 01/2008 to 01/2019 (mean age 21.4 years, 51 % ♀, 49 % ♂) with suspected EBV infection was performed. The groups of a serologically confirmed or excluded EBV infection were compared.

An automated differential blood count was available in n = 42 patients with primary EBV infection. Average lymphocyte count was 5.5 ± 2.6 giga/l. Patients with acute bacterial tonsillitis (n = 36) had significantly lower values with 1.6 ± 1.3 giga/l, p < 0.05. Equal results were found in relative lymphocyte counts (47.4 ± 17.9 vs. 12.8 ± 9.1 %, p < 0.05). For monocyte counts, neither absolute (1.2 ± 0.8 vs. 1.2 ± 0.6 giga/l, p = 0.617) nor relative (8.8 ± 3.6 vs. 9.8 ± 5.2 %, p = 0.746) monocyte counts showed significant differences.

Increased lymphocyte counts in an automated differential blood count can be a first indication of primary EBV infection. Perhaps up to 30 % morphologically altered lymphocytes are increasingly counted correctly with modern hematology analyzers and no longer counted as monocytes. These results could be used to make decisions about further diagnosis (abdominal ultrasonography, ECG) and antibiotic therapy before results of EBV serology are available.