Effects of bacteria and yeast on WBC counting in three automated hematology counters

Bacteria or yeast may be observed on peripheral blood smears and may lead to spuriously elevated platelet counts. They have been reported to disturb the white blood cell (WBC) differential count if they clumped together, and a large number of such microorganisms have been shown to increase WBC counts. The purpose of this study was to evaluate the spurious rise in WBC counts according to species of microorganisms and automated hematology analyzers. The species we selected were Staphylococcus aureus, Escherichia coli, Candida albicans, C. tropicalis, C. krusei, C. dubliniensis, C. glabrata, and C. parapsilosis. We investigated the effects of bacteria and yeast on peripheral blood samples by the ADVIA 120/2120 Hematology System, Sysmex XE-2100 (TOA Medical Electronics, Kobe, Japan) and Coulter LH 750 (Beckman Coulter, Miami, FL, USA). C. albicans, C. tropicalis, C. krusei, and C. dubliniensis had an overt effect on the WBC count at concentrations of up to 1–5 × 10⁷ colony-forming units (CFU)/mL in three automated cell counters, and C. glabrata and C. parapsilosis, when present at concentrations of 1–5 × 10⁸ CFU/mL, caused a significant increase in the WBC count obtained by the Sysmex XE-2100 but not by the ADVIA 120/2120 system and Coulter LH 750 (p < 0.05). In conclusion, yeast may influence the results of peripheral blood smears only when the yeast concentration is unusually high. The results differed among analyzers and among species of yeast. Hematologists should be aware that samples containing bacteria and yeast may give erroneously high WBC counts and differential leukocyte counts and should review the peripheral blood smear by microscopy.