Evaluation of six cytometric methods for reticulocyte enumeration and differentiation in the cat

Six protocols utilizing three fluorescent nucleic acid dyes (thiazole orange, auramine 0, and acridine orange) were evaluated by flow cytometty for clinical utility in the analysis of feline reticulocytes. The dyes showed good to poor correlations with each other and with manual counts. Thiazole orange was the preferred stain. Thiazole orange dye showed distinct peaks corresponding to aggregate and punctate reticulocytes from specimens with marked reticulocytosis. The other dyes detected increases in reticulocyte numbers but subpopulations could not be distinguished. Standardized instrument and gate settings, applied to specimens stained with thiazole orange dye, enumerated aggregate and punctate reticulowes in low celfularity specimens that lacked distinct peaks. Percentages of these cells correlated well with manual counts, offering a simplified technique for routine laboratory use.