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KMID : 1011820170580050378
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Investigative and Clinical Urology
2017 Volume.58 No. 5 p.378 ~ p.382
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Optimization of urinary dipstick pH: Are multiple dipstick pH readings reliably comparable to commercial 24-hour urinary pH?
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Abbott Joel E.
Miller Daniel L.
Shi William
Wenzler David
Elkhoury Fuad F.
Patel Nishant D.
Sur Roger L.
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Abstract
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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.
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KEYWORD
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Kidney calculi, Nephrolithiasis, Prevention and control, Urine specimen collection
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