Comparison between the urine dipstick and the pH-meter to assess urine pH in sheep and dogs

Abstract

Background: Urine pH is an integral part of a complete urinalysis, and is commonly measured in veterinary practice using semiquantitative reagent strips. Objective: The aim of this study was to compare the urine pH of dogs and sheep, using visual interpretation of dipstick reactions, and using a pH-meter as the reference method. Agreement between the 2 methods was also assessed. An additional objective was to compare the urine pH before and after centrifugation. Methods: A total of 50 voided urine samples from sheep and 52 from dogs were collected into sterile containers. For pH measurements, 2 methods were used, a pH-meter and urine dipstick reagent pads. Measurements were performed using urine samples before (whole urine) and after centrifugation (urine supernatant). For comparison of the 2 methods, Passing and Bablok regression analysis and Bland–Altman plots were used. Results: The equation created to assess agreement between the 2 methods in dogs showed a constant bias at −0.14 and a positive proportional bias at 0.98. From a clinical standpoint, total bias was below and above the maximum acceptable bias in sheep and dogs, respectively. Clinically acceptable bias was also found using centrifuged urine samples in sheep, but the urine pH values before and after centrifugation were nearly identical in dogs. Conclusion: Urine dipstick reagent pads and pH-meters can be used interchangeably to determine urine pH in sheep without needing centrifugation. In contrast, pH-meters provide more accurate pH measurements than urine dipstick pads in canine urine, which is not improved by centrifugation. © 2018 American Society for Veterinary Clinical Pathology