Abnormalities of leukocyte histograms resulting from microorganisms

The authors report a series of 13 patients seen in their laboratory during October 1985 to August 1988 in which the presence of bacterial, fungal, or malarial parasites visible on peripheral smear was correlated with an abnormal leukocyte histogram. Samples submitted for complete blood count and differential counts were analyzed with Coulter S-Plus VI (seven specimens) or S-Plus STKR (six specimens) instrumentation. Organisms visualized on the Wright-stained peripheral smears included Histoplasma capsulatum (two), Candida sp. (four), Plasmodium sp. (three), and Staphylococcus sp. (four). Two patients had a diagnosis of acquired immune deficiency syndrome (AIDS); intravascular catheters were present in five other patients. In all cases the leukocyte histograms were abnormal. The instrument flagged abnormalities of the R1 region in four patients and multiple regions in nine patients. Similar flags were produced by the in vitro addition of bacteria or fungi to whole blood. These studies document that the presence of microorganisms in the peripheral blood can result in spurious white blood cell (WBC) counts or electronic differentials. The authors' findings indicate that the possibility of circulating organisms should be considered when abnormal WBC flags are detected with Coulter instrumentation.