Optimization of urinary dipstick pH: Are multiple dipstick pH readings reliably comparable to commercial 24-hour urinary pH?

Abstract

PurposeAccurate measurement of pH is necessary to guide medical management of nephrolithiasis. Urinary dipsticks offer a convenient method to measure pH, but prior studies have only assessed the accuracy of a single, spot dipstick. Given the known diurnal variation in pH, a single dipstick pH is unlikely to reflect the average daily urinary pH. Our goal was to determine whether multiple dipstick pH readings would be reliably comparable to pH from a 24-hour urine analysis.Materials and MethodsKidney stone patients undergoing a 24-hour urine collection were enrolled and took images of dipsticks from their first 3 voids concurrently with the 24-hour collection. Images were sent to and read by a study investigator. The individual and mean pH from the dipsticks were compared to the 24-hour urine pH and considered to be accurate if the dipstick readings were within 0.5 of the 24-hour urine pH. The Bland-Altman test of agreement was used to further compare dipstick pH relative to 24-hour urine pH.ResultsFifty-nine percent of patients had mean urinary pH values within 0.5 pH units of their 24-hour urine pH. Bland-Altman analysis showed a mean difference between dipstick pH and 24-hour urine pH of -0.22, with an upper limit of agreement of 1.02 (95% confidence interval [CI], 0.45–1.59) and a lower limit of agreement of -1.47 (95% CI, -2.04 to -0.90).ConclusionsWe concluded that urinary dipstick based pH measurement lacks the precision required to guide medical management of nephrolithiasis and physicians should use 24-hour urine analysis to base their metabolic therapy.

Measurement of urine pH and net acid excretion and their association with urine calcium excretion in periparturient dairy cows

“…More importantly, the Bland-Altman plot indicated that the dipstick measured urine pH 0.28 units higher than the reference method, which was within the limits of acceptability of ≤0.50 pH units. The small positive bias was similar to that reported in dog urine (+0.22; Johnson et al, 2007) but different from findings in other species, where a bias of −0.22 was identified in human urine (Abbott et al, 2017), −0.02 in sheep urine (Athanasiou et al, 2018), and −0.12 in cat urine (Raskin et al, 2002). The difference in analytical performance of the dipstick may be due to species differences in urine color.…”

“…The acceptable limits for U pH-MS and U pH-HP were considered to be ≤0.5 pH units compared with the reference method (U pH ). Acceptable limits were based on the results of other studies (Heuter et al, 1998;Kwong et al, 2013;Abbott et al, 2017), the resolution of U pH-MS measurement, and personal observations that variations in U pH of this magnitude commonly occur over a 24-h period in cattle fed a TMR.…”

Analytical verification of 12 most commonly used urine dipsticks in Croatia: comparability, repeatability and accuracy

“…Various dipsticks may differ in their diagnostic performance regarding leukocyte and erythrocyte detection ( 5 ). There is also evidence that urine dipstick pH analysis shows insufficient accuracy ( 6 ).…”

Evaluation of a Portable Urinary pH Meter and Reagent Strips

“…Urinary pH varies throughout the day and the decision to acidify or alkalize urine is generally not based on an isolated urine sample. [15][16][17] It is important that caregivers and patients possess accurate pH measuring devices. Since pH is a logarithmic scale, an increase in one pH unit means a tenfold decrease in acidity or hydrogen-ion concentration.…”