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Evaluation of the reproducibility and accuracy of pH-determining devices used to measure urine pH in dogs

Kristen Y. Johnson BA1, Jody P. Lulich DVM, PhD, DACVIM2, and Carl A. Osborne DVM, PhD, DACVIM3
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  • 1 Minnesota Urolith Center, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.
  • | 2 Minnesota Urolith Center, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.
  • | 3 Minnesota Urolith Center, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108.

Abstract

Objective—To evaluate the reproducibility and accuracy of 4 portable pH meters, a reagent strip, and pH paper for measuring urine pH in dogs.

Design—Prospective masked randomized study.

Sample Population—201 free-catch urine samples from 114 hospitalized dogs.

Procedures—Urine samples were divided into 2-mL aliquots. Measurements of urine pH were obtained by use of a laboratory benchtop pH meter, 4 portable pH meters, a urine reagent strip, and pH paper. The pH of each aliquot was measured within 4 hours of collection by an evaluator unaware of the aliquot's origin.To assess reproducibility, the coefficient of variation for each pH measurement device was calculated. To determine which device was most accurate, the degree of agreement among the different devices was assessed in comparison with the benchtop pH meter, which was considered the reference method.

Results—3 of the 4 portable pH meters had nearly perfect agreement with the reference method. The reagent strip and pH paper had moderate to poor agreement with the reference method.

Conclusions and Clinical Relevance—Urine pH measurements should be made by use of a portable or benchtop pH meter when accurate measurements are crucial for diagnosis or treatment. Reagent strips and pH papers are useful in obtaining pH approximations but are not recommended when accurate measurements of urine pH are required.

Abstract

Objective—To evaluate the reproducibility and accuracy of 4 portable pH meters, a reagent strip, and pH paper for measuring urine pH in dogs.

Design—Prospective masked randomized study.

Sample Population—201 free-catch urine samples from 114 hospitalized dogs.

Procedures—Urine samples were divided into 2-mL aliquots. Measurements of urine pH were obtained by use of a laboratory benchtop pH meter, 4 portable pH meters, a urine reagent strip, and pH paper. The pH of each aliquot was measured within 4 hours of collection by an evaluator unaware of the aliquot's origin.To assess reproducibility, the coefficient of variation for each pH measurement device was calculated. To determine which device was most accurate, the degree of agreement among the different devices was assessed in comparison with the benchtop pH meter, which was considered the reference method.

Results—3 of the 4 portable pH meters had nearly perfect agreement with the reference method. The reagent strip and pH paper had moderate to poor agreement with the reference method.

Conclusions and Clinical Relevance—Urine pH measurements should be made by use of a portable or benchtop pH meter when accurate measurements are crucial for diagnosis or treatment. Reagent strips and pH papers are useful in obtaining pH approximations but are not recommended when accurate measurements of urine pH are required.

Contributor Notes

Presented as an abstract at the 24th Annual American College of Veterinary Internal Medicine Forum, Louisville, Ky, May 2006.

Address correspondence to Dr. Lulich.