METABOLIC URINARY CORRELATES OF CALCIUM-OXALATE DIHYDRATE IN RENAL STONES

Purpose: We determined what metabolic features of the 24-hour urine pr edict calcium oxalate dihydrate in kidney stones. Prior studies have s uggested that low urine magnesium, high urine calcium, high calcium-to -oxalate ratio and high urine supersaturation with respect to calcium oxalate monohydrate predict calcium oxalate dihydrate. Materials and M ethods: Stone analyses and results from 2, 24-hour pretreatment urine collections from 96 patients with nephrolithiasis were drawn from 3 ki dney stone prevention centers. Standard stone risk measurements were m ade on the urine, including supersaturation for calcium oxalate monohy drate, brushite and uric acid. Results: The main differences in metabo lic urine findings were between patients with no calcium oxalate dihyd rate and those with any calcium oxalate dihydrate in stones. Percent c alcium oxalate dihydrate itself did not correlate with urine findings, Patients with no calcium oxalate dihydrate in stones showed a biphasi c pattern of urine calcium oxalate monohydrate supersaturation, about half had values below almost any found among patients with calcium oxa late dihydrate in stones (less than 7) and the rest overlapped with th e calcium oxalate dihydrate group. Except for higher calcium oxalate m onohydrate supersaturation, patients with calcium oxalate dihydrate in stones had higher urine calcium excretion and lower urine citrate con centrations, even after calcium oxalate monohydrate supersaturation wa s considered. Conclusions: Patients with low calcium oxalate monohydra te supersaturation (less than 7) are unlikely to have calcium oxalate dihydrate in renal stones. However, many patients with no calcium oxal ate dihydrate have higher calcium oxalate monohydrate supersaturation values, and so prediction of calcium oxalate dihydrate or its absence from urine findings is imperfect. Urine magnesium and the calcium-to-o xalate ratio are unrelated to calcium oxalate dihydrate.