Comparison of six microscopic methods and two operators for estimation of white and red blood cells in canine urine sediment.

Abstract

Little information is currently available about the analytical variability of urinalysis. We aimed to compare results obtained by two operators using six microscopic methods in the quantification of urinary leukocytes (WBC) and erythrocytes (RBC). Forty urine samples (10mL) were centrifuged (450g, 5minutes) and resuspended in 0.5mL of supernatant. Two operators with different expertise in urinalysis interpreted sediment results using the six methods, obtained by combining the use of microscope slides (Slide) or counting chambers (Chamber) with three different techniques: bright-field (BF) microscopy, phase-contrast (PC) microscopy, and stained sediment (SS) evaluations. The mean WBC and RBC counts from 10 fields (Slide) or squares (Chamber) observed at 400× were used to calculate the difference and agreement between operators and methods. We also estimated the concordance between methods in classifying microhematuric or pyuric samples. Operator 2 counted significantly lower WBC counts using Slide+BF (P= 0.009) and Slide+PC (P= 0.001) than Operator 1, whereas no inter-operator differences were recorded for RBC counts. The concordance between the operators ranged from "good" to "very good." No differences or biases were found for WBC counts among the methods, and concordances were "good" to "very good"; proportional biases were found for RBC counts between Slide+BF vs Slide+SS and Slide+PC vs Slide+SS. Concordance measurements for RBC counts ranged from "good" to "very good." All methods yielded good reproducibility among operators, although stained SS evaluations allowed better identification of WBC by the inexperienced operator. However, we suspected that the SS preparations affected RBC counts. All other methods yielded reproducible WBC and RBC counts.