Baseline Urinary Calcium and the Efficacy of Thiazide Diuretics for Kidney Stone Prevention

Previous studies have shown that thiazide diuretics' ability to decrease symptomatic stone events depends on the extent to which they reduce urine calcium. However, it remains unknown whether the calcium change from thiazide diuretics depends on the baseline urine calcium level.

Among a cohort of Medicare beneficiaries with a 24-hour urine collection for kidney stone disease processed by Labcorp/Litholink between 2011 and 2018, we identified a subset aged > 18 years newly prescribed a thiazide diuretic who performed a second collection between 30 and 180 days after their initial prescription fill. We then fit multivariable linear regression models to estimate the association between dose of thiazide prescribed and change in urine calcium, stratifying by baseline urine calcium. We compared cumulative incidences of clinical stone events stratified by baseline urine calcium groups within a treated and untreated cohort.

From a total of 634 participants, higher baseline urine calcium was associated with greater 24-hour mean absolute (in mg/d) and percentage urine calcium reductions (P_trend < 0.001 for both). Higher thiazide dose was associated with greater absolute and percentage urine calcium reduction. No statistically significant differences were seen comparing the adjusted incidences of clinical stone events across baseline calcium groups after thiazide prescription. However, among individuals without thiazide exposure, the unadjusted and adjusted cumulative incidences were higher with greater baseline urine calcium (both P_trend < 0.001).

Greater urine calcium reductions after thiazide treatment are observed among those with higher baseline urine calcium, and higher thiazide dose led to a larger reduction. These data are relevant for individualizing thiazide dose for kidney stone prevention.