Accuracy of urine pH testing in a regional metabolic renal clinic: is the dipstick accurate enough?

Abstract

Urine pH is a useful marker for assessing treatment need and efficacy in patients with nephrolithiasis. Though the gold standard of measurement is with a pH electrode, dipsticks offer the convenience of cost, ease of use, and the possibility of patients measuring their own values outside the clinic. The aim of this study was to determine whether dipsticks offer the same accuracy as the electrode. Paired measurements of freshly voided urine pH with both electrode and dipstick were analysed in a multidisciplinary renal clinic. We found that although there was a high Pearson correlation between the samples (0.89, p = 0.001), urine dipstick measurements carried an approximately 1 in 4 risk of producing clinically significant differences (pH differences > 0.5 pH unit) from meter values. We also found that at high and low urine pH, the dipstick tended to over- and underestimate true pH readings, respectively. Examining the values in the 98 patients where a need for pharmacological urinary pH manipulation was indicated by the true pH, we found 14 who would not have been appropriately treated, and 5 who would have been unnecessarily medicated, if the stick pH value had been used. We conclude that dipstick pH measurement is insufficiently reliable for guiding clinical decision-making.

Clinical Usefulness of pH Papers in the Measurement of Salivary pH

“…14,15,[22][23][24] There are two reasons for this. First, validity of measurement with pH paper can be influenced by several factors such as color blindness of the reader, environmental lighting, and the presence of blood, chemical factors and proteins reacting with pH paper.…”

“…4,6) Salivary pH can be measured by pH paper or pH meter. 14) Despite the current status of pH meter as a gold standard in the pH measurement, some problems limit the clinical access to use it. 15) First, pH meter is relatively expensive, and needs regular calibration, test solution, and user training.…”

“…14) However, studies on the reproducibility of pH paper is few and reliability should be taken into consideration prior to discussing the clinical usefulness of pH paper. Besides, researches to determine whether pH paper is an alternative to pH meter for salivary pH measurement should be performed because there are only a few researches for saliva while there have been a number of studies for other bodily fluids.…”

“…Besides, researches to determine whether pH paper is an alternative to pH meter for salivary pH measurement should be performed because there are only a few researches for saliva while there have been a number of studies for other bodily fluids. 14,15) Therefore, the aim of this study was to evaluate the reliability of the salivary pH measurement using pH paper. The normal values of salivary pH using pH paper were compared to those of pH meter to investigate the validity.…”

Review of the Diagnostic Evaluation of Normal Anion Gap Metabolic Acidosis

“…Because urine can achieve a hydrogen ion concentration 1,000× greater than blood, its pH ranges from 4.5 to 8 (average pH 5-6) [36] . Though the gold standard of measurement is with a pH electrode, dipsticks offer the convenience of cost and ease of use [37] . However, many limitations concerning the urine pH level exist.…”