Differential 24h urine findings in predominantly calcium oxalate monohydrate stones
Kaylee Luck, MD, MS, Meg Hanley, BS, Emily May, BS, Vernon M. Pais, Jr., MD.
Dartmouth Hitchcock, Lebanon, NH, USA.
BACKGROUND: Calcium oxalate monohydrate (COM) stones are among the most commonly encountered. Debate continues whether selective or empiric medical therapy is preferable. The American College of Physicians has recommended empiric pharmacologic monotherapy including thiazide for those with active stone disease despite increased fluid intake without 24hour urine testing. However, it is unclear whether such empiric therapy can adequately target underlying abnormalities in a diverse group of patients. We assessed baseline 24hour urine parameters in those with COM-containing stones.
METHODS: We collected data on adult patients from 2011-2022 who were evaluated for nephrolithiasis at a single institution and had complete 24 hour urine analysis evaluation. A complete 24 hour urine included measurements for pH, total volume, calcium, oxalate, citrate, uric acid, sodium, potassium and creatinine. We excluded patients less than 18 years of age. Data was analyzed using STATA v 14.0. Continuous variables were expressed as mean with standard deviation.
RESULTS: Of the 541 patients, 274 were female (50.1%). The mean age of the patients was 55 years (standard deviation of 14.8 years). The mean BMI was 29.7 (standard deviation of 8). From this cohort, 232 consecutive patients with COM containing stones and 24h urine collections were subsequently analyzed.Those with predominant (>80%) COM had significantly lower 24hour urine calcium (mg/d) than those with mixed CaOx (179 vs 228, p=0.0009) on initial 24 hour urine. Furthermore, this group had higher 24hour urinary oxalate (mg/d) than those with mixed CaOx (39 vs 34, p=0.03).CONCLUSIONS:COM stones are characterized by lower urinary calcium and higher urinary oxalate than those with mixed calcium oxalate stones. As such, predominant COM stones represent a discrete phenotype which may not benefit from empiric treatment with calcium-lowering measures such as thiazide. Empiric thiazide treatment of COM stone formers in the absence of documented hypercalciuria may pose unnecessary expense as well as exposure to potential side effects
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