Accurate and consistent results in monitoring urine pH are essential for proper diagnosis and treatment of many diseases. For example, urine pH is important in interpretation of findings in urine sediment. Urine pH may also influence the risk of urolith formation in susceptible animals and reflect systemic acid-base abnormalities. Commercially available urine reagent strips are commonly used to determine urine pH in veterinary patients because of their convenience and low cost. However, urine reagent strips may not be sufficiently accurate for evaluation of some diseases.1,2 Portable pH meters have been advocated as an accurate alternative to reagent strips and a relatively inexpensive alternative to benchtop pH meters. Benchtop pH meters contain special electrodes that allow hydrogen ions in a solution to move through a selective barrier, eliciting a measurable voltage proportional to the solution's pH.3 To confirm these findings, the present study was designed to compare the reproducibility and accuracy of 4 portable pH meters in measuring urine pH for use in veterinary medicine. Reproducibility is defined as the ability to obtain the same value for repeated measurements of the same analyte in a sample4 and is synonymous with measurement precision. Poor reproducibility degrades the precision of a single measurement by impairing the observer's ability to discriminate change. Accuracy is defined as the ability to obtain the established or true value of an analyte in a sample and verifies the correctness of a test result.4
Clinical and Laboratory Standards Institute
pH meter 430, Corning, Corning, NY.
Checker 1, Hanna Instruments, Woonsocket, RI.
Oakton waterproof pH tester BNC, Oakton Instruments, Vernon Hills, Ill.
Extech waterproof palm pH meter, model PH 220, Extech Instruments, Waltham, Mass.
Omega PHH-5012, Omega Engineering, Stamford, Conn.
Multistix, Bayer Corp, Elkhart, Ind.
pHydrion Vivid 1-11, Micro Essential Laboratory, Brooklyn, NY.
Buffer pH 4.0, EMD Chemicals Inc, Gibbstown, NJ.
Buffer pH 7.0, EMD Chemicals Inc, Gibbstown, NJ.
Copolymer plastic vial, 7 mL unlined, Research Products International, Mount Prospect, Ill.
Raskin RE, Murray KA, Levy JK. Comparison of home monitoring methods for feline urine pH measurement. Vet Clin Pathol 2002;31:51–55.
Heuter KJ, Buffington CA, Chew DJ. Agreement between two methods for measuring urine pH in cats and dogs. J Am Vet Med Assoc 1998;213:996–998.
Sensorex Corporation Web site. pH Electrode Technical Education, 2006. Available at: www.sensorex.com/support/education/pH_education.html. Accessed Aug 7, 2006.
Osborne CA, Stevens JB. “Prophet”-ing more from urinalysis: maximizing reproducible test results. In: Osborne CA, Stevens JB, eds.Urinalysis: guide to compassionate patient care. Shawnee Mission, Kan: Bayer Co, 1999;51–63.
Osborne CA, Stevens JB. Biochemical analysis of urine: indications, methods, interpretation. In: Osborne CA, Stevens JB, eds.Urinalysis: guide to compassionate patient care. Shawnee Mission, Kan: Bayer Co, 1999;88–92.
Ryan JP, Irwin JA. Practical studies on urine demonstrating principles of clinical and veterinary significance. Biochem Mol Biol Educ 2002;30:98–100.
Motlusky H. The standard deviation. In: Moltusky H, ed. Intuitive biostatistics. New York: Oxford University Press, 1995;22–30.
Motlusky H. Comparing two paired groups: paired t and wilcoxon tests. In: Moltusky H, ed. Intuitive biostatistics. New York: Oxford University Press, 1995;225–229.
National Committee for Clinical Laboratory Standards. Method comparison and bias estimation using patient samples, approved guideline. NCCLS EP9-A. Wayne, Pa: NCCLS, 1995.
Buffington CA, Rogers QR, Morris JG. Effect of diet on struvite activity product in feline urine. Am J Vet Res 1990;51:2025–2029.
Kirk CA, Ling GV, Franti CE, et al. Evaluation of factors associated with development of calcium oxalate urolithiasis in cats. J Am Vet Med Assoc 1995;207:1429–1434.
Lekcharoensuk C, Osborne CA, Lulich JP, et al. Association between dietary factors and calcium oxalate and magnesium ammonium phosphate urolithiasis in cats. J Am Vet Med Assoc 2001;219:1228–1237.
Strom JG Jr, Jun HW. Effect of urine pH and ascorbic acid on the rate of conversion of methenamine to formaldehyde. Biopharm Drug Dispos 1993;14:61–69.
Unwin RJ, Shirley DG, Capasso G. Urinary acidification and distal renal tubular acidosis. J Nephrol 2002;15 (suppl 5):S142–S150.