Evaluation of a Portable Urinary pH Meter and Reagent Strips.

Abstract

To evaluate a portable electronic pH meter and to put its accuracy in perspective with reagent strips read by a layperson, a healthcare professional, and an electronic reading device. Based on a preanalysis on 20 patients, a sample size of 77 urine aliquots from healthy volunteers was necessary to obtain sufficient study power. Measurements of urinary pH were obtained by use of reagent strips, a portable pH meter and a laboratory pH meter (gold standard). Reagents strips were read by a professional experienced in interpreting strips, a layperson, and an electronic strip reader. The mean matched pair difference between measurement methods was analyzed by the paired t-test. The degree of correlation and agreement were evaluated by the Pearson's correlation coefficient and Bland-Altman plots, respectively. The mean matched pair difference between the gold standard and all other pH measurement methods was the smallest with the portable electronic pH meter (bias 0.01, 95% confidence interval [CI] -0.07 to 0.08; p = 0.89), followed by strips read by a professional (bias -0.09, 95% CI -0.21 to 0.02; p = 0.10), layperson (bias -0.17, 95% CI -0.31 to -0.04; p = 0.015), and electronic strip reader (bias -0.29, 95% CI -0.41 to -0.16; p < 0.001). The portable electronic pH meter achieved the highest Pearson's correlation coefficient and narrowest 95% limits of agreement, followed by strip interpretation by a professional, electronic strip reader, and layperson. To quantify the ability of pH measurement methods to correctly classify values within a predefined urinary pH target range, we performed classification tests for several stones. The portable electronic pH meter outperformed all other measurement methods for negative predictive values. Findings of this study support that the portable electronic pH meter is a reliable pH measuring device. It appears to be more accurate compared to reagent strips readings.