Comparison of white and red blood cell estimates in urine sediment with hemocytometer and automated counts in dogs and cats

Abstract

Therapeutic decisions regarding urinalysis are commonly based on the presence of white and red blood cells. Traditionally, numbers per high-power field are estimated using wet-mount microscopic examination. This technique is not standardized and counts are likely prone to inaccuracy. In addition, differentiation of leukocyte types is not possible. The aims of this study were to (1) compare WBC and RBC estimates using wet-mount examination with counts obtained using a hemocytometer, (2) assess if a hematology automated analyzer (Sysmex ST-2000iV/XT) provides reliable WBC and RBC counts in urine comparable to hemocytometer counts, and (3) evaluate air-dried Wright-Giemsa-stained urine drop sediment preparations for the determination of differential leukocyte counts. WBC and RBC counts were obtained by performing wet-mount estimates, manual hemocytometer counts, and Sysmex automated counts on 219 canine and feline urine samples. Results were correlated using Spearman rank correlation. Air-dried Wright-Giemsa stained sediment drop preparations (n = 215) were examined for differential counts of leukocytes. A low but significant association was found between WBC estimates on wet-mount examination and hemocytometer counts (rho = 0.37, P < .01). There was a high and significant association when RBC counts were compared between wet-mount and hemocytometer evaluation (rho = 0.7, P < .01). There was very high and significant interassay correlation between Sysmex data from duplicate samples for what the analyzer classified as WBC (rho = 0.97, P < .01) and RBC (rho = 0.94, P < .01). Low correlations were found between the Sysmex RBC counts and both wet-mount estimates and hemocytometer RBC counts (rho = 0.43, P < .01 and rho = 0.39, P < .01, respectively). Cell preservation in the air-dried sediment preparations was so poor that differential counts could not be performed. WBC and RBC estimates on wet-mount examination agreed with hemocytometer counts and are therefore considered adequate. The Sysmex ST-2000iV/XT did not provide reliable cell counts under the conditions used.