Investig Clin Urol.  2017 Sep;58(5):378-382. 10.4111/icu.2017.58.5.378.

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

• Abbott JE
• Miller DL
• Shi W
• Wenzler D
• Elkhoury F
• Patel ND
• Sur RL

• KMID: 2388056
• DOI: http://doi.org/10.4111/icu.2017.58.5.378

Abstract

PURPOSE
Accurate 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 METHODS
Kidney 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.
RESULTS
Fifty-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).
CONCLUSIONS
We 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.

Keyword

Kidney calculi; Nephrolithiasis; Prevention and control; Urine specimen collection

MeSH Terms

Humans
Hydrogen-Ion Concentration*
Kidney Calculi
Methods
Nephrolithiasis
Reading*
Research Personnel
Urine Specimen Collection

Figure

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  Fig. 1 Bland-Altman plot comparing the mean of 3 dipstick pH readings with the concurrent 24-hour urine pH.

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  Fig. 2 Bland-Altman plot comparing the dipstick pH from the first void of the day with the concurrent 24-hour urine pH.

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  Fig. 3 Bland-Altman plot comparing the dipstick pH from the second void of the day with the concurrent 24-hour urine pH.

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  Fig. 4 Bland-Altman plot comparing the dipstick pH from the third void of the day with the concurrent 24-hour urine pH.

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