Urine pH measurement is performed during routine urine analysis evaluation. Although using a pH meter has been shown to give more accurate results, urine dipsticks are most commonly used in veterinary medicine. Accurate pH measurement is important, as it may indicate urinary infection, risk of urolith formation and reflect the acid-base systemic status of a patient. This study evaluated the inter-operator reproducibility of canine urine pH readings when performing urine dipstick chemical analysis by direct standard visualization and automated analysis in a small animal teaching hospital.

Urine from in-patients was collected between 28 and 40 hours prior to the study and was kept refrigerated. The pooled sample was divided in three and each sample was titrated with NaOH and HCl to achieve a consistent visual urine dipstick pH reading of 6 (Sample 1), 7 (Sample 2) and 7.5 (Sample 3). Respective readings of 5.44, 6.55 and 7.66, were obtained with a calibrated reference bench top pH meter. Samples were kept chilled during the study period.

Study participants were given one aliquot each sample and six urine dipsticks. Each operator was asked to measure and record the urine pH from each aliquot using first standard visual and then automated analyser reading methods.

Nineteen final year students, 7 veterinarian surgeons and 4 veterinary nurses participated in the study. Standard visual reading pH values, with number of participants recording the results in brackets, were: Sample 1: 6 (14), 6.5 (14), 7 (2); Sample 2: 6 (2), 6.5 (2), 7 (1), 7.5 (22), 8 (3); and Sample 3: 6 (1), 7 (1), 7.5 (3), 8 (25). Using the automated analyser, the results obtained were: Sample 1: 5.5 (1), 6 (29); Sample 2: 7 (26), 7.5 (4); Sample 3 7 (1), 7.5 (25), 8 (3), 8.5 (1). Concordance of results between study participants and the authors occurred in 39/90 (43%) of visually read, and 79/90 (88%) of automated analyser results. Sample 2 was visually reported as alkaline (pH of 8) by 4 participants and acid (pH of 6) by 2 participants.

In conclusion, standard visual reading of urinary dipstick demonstrated poorer inter-operator reproducibility when measuring canine urinary pH in comparison with an automated method. This has potential clinical implications in that the same sample was classified as acidic and alkaline in some instances, potentially affecting clinical decision making.

Disclosures

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