Evaluation of a standardized procedure for counting microscopic cells in body fluids

Abstract

A standardized urinalysis and manual microscopic cell counting system was evaluated for its potential to reduce intra‐ and interoperator variability in urine and cerebrospinal fluid (CSF) cell counts. Replicate aliquots of pooled specimens were submitted blindly to technologists who were instructed to use either the Kova system with the disposable Glasstic slide (Hycor Biomedical, Inc., Garden Grove, CA) or the standard operating procedure of the University of California–Irvine (UCI), which uses plain glass slides for urine sediments and hemacytometers for CSF. The Hycor system provides a mechanical means of obtaining a fixed volume of fluid in which to resuspend the sediment, and fixes the volume of specimen to be microscopically examined by using capillary filling of a chamber containing in‐plane counting grids. Ninety aliquots of pooled specimens of each type of body fluid were used to assess the inter‐ and intraoperator reproducibility of the measurements. The variability of replicate Hycor measurements made on a single specimen by the same or different observers was compared with that predicted by a Poisson distribution. The Hycor methods generally resulted in test statistics that were slightly lower than those obtained with the laboratory standard methods, indicating a trend toward decreasing the effects of various sources of variability. For 15 paired aliquots of each body fluid, tests for systematically higher or lower measurements with the Hycor methods were performed using the Wilcoxon signed‐rank test. Also examined was the average difference between the Hycor and current laboratory standard measurements, along with a 95% confidence interval (CI) for the true average difference. Without increasing labor or the requirement for attention to detail, the Hycor method provides slightly better interrater comparisons than the current method used at UCI. J. Clin. Lab. Anal. 19:267–275, 2005. © 2005 Wiley‐Liss, Inc.