24-Hour Urine Testing for Nephrolithiasis: Interpretation and Treatment Guidelines

Excerpt

Roughly half of all symptomatic renal calculi are potentially preventable with proper diagnosis and treatment for underlying chemical stone-promoting risk factors. There is little question that our current medical evaluation and prophylactic therapy for recurrent nephrolithiasis is underutilized and generally inadequate. In 2012, the annual direct and indirect costs of nephrolithiasis were estimated at over $10 billion. This figure is predicted to exceed $15 billion by 2030 due to general population growth and the increasing prevalence of risk factors, such as diabetes, metabolic syndrome, and obesity, for kidney stones. In addition, quality of life scores are dramatically lowered in patients with nephrolithiasis, even in those with asymptomatic stones.

Second only to actual kidney stone analysis, the 24-hour urine test is the most useful diagnostic test for nephrolithiasis prophylaxis. In a comprehensive study involving nearly 29,000 individuals at high risk for nephrolithiasis, only 7.4% of patients underwent 24-hour urine testing within 6 months of their kidney stone. Nephrolithiasis patients were 3 times more likely to undergo 24-hour urine testing if a nephrologist or urologist treated them compared to a primary care physician. Repeat testing within 6 months of the initial 24-hour urine test, which is highly recommended to verify treatment efficacy and compliance, was only 16%. Multiple reasons underlie testing underuse. Similar to all 24-hour urine collection tests, it drastically limits activities on the day of the specimen collection; therefore, this can be tedious. Portions of the urinary chemistry are sometimes sent to different reference laboratories, often leading to unacceptable delays and incomplete results that cannot be easily interpreted. The most critical results are usually buried amid paragraphs of obligatory boilerplate, making it almost impossible to identify. Even worse, results are often presented as 24-hour totals that are either high or low or normal or abnormal without regard for concentration, pH, or the optimal levels of these chemistries.

After the critical data are available, analysis and treatment selection must still be conducted. Evaluating and interpreting the laboratory results are often erroneously perceived as overly complicated. Even experienced experts may find it challenging to locate and clarify critical data. This review aims to streamline the analysis and evaluation of a 24-hour urine collection and treatment selection, thereby empowering practitioners to feel more confident in using and interpreting this important test for patients with nephrolithiasis.