Metabolic syndrome and the risk of calcium stones.

BACKGROUND The metabolic syndrome (MS) is associated with increased prevalence of kidney stones, yet the specific stone type remains largely unknown. This study was conducted to assess whether risk factors associated with calcium nephrolithiasis increase with individual characteristics of the MS. METHODS A retrospective analysis was performed in 109 non-stone-forming subjects and 128 recurrent calcium stone formers from Dallas, Texas. A separate analysis was performed in 140 recurrent calcium stone formers from Bern, Switzerland. Demographic, anthropometric, serum and urinary profiles were measured. RESULTS In non-stone formers from Dallas, urinary calcium (3.6 ± 1.8 to 6.0 ± 2.9 mmol/day, P = 0.0003 for trend, zero to four features) increased with increasing features of the MS. This change was attendant with a significant rise in supersaturation index (SI) of calcium oxalate (CaOx) (2.76 ± 1.21 to 4.45 ± 1.65, P < 0.0001; zero to four features). In calcium stone formers from Dallas, urinary calcium marginally increased (5.2 ± 2.3 to 7.0 ± 4.0 mmol/day, P = 0.09; zero to four features), while urinary oxalate (356 ± 141 to 504 ± 203 μmol/day, P = 0.001; zero to four features) and SI CaOx (4.46 ± 1.80 to 6.16 ± 3.71, P = 0.009; zero to four features) significantly increased with features of the MS. However, when adjusted for confounding variables such as total volume, age, gender, urine sodium and urine sulfate, urinary calcium and SI CaOx showed no significant changes in stone formers yet remained significant in non-stone formers. In a separate cohort from Bern, Switzerland urinary calcium (6.9 ± 3.6 versus 7.0 ± 3.2, P = 0.8) and SI CaOx (3.37 ± 1.98 versus 4.04 ± 2.78, P = 0.5) did not differ between subjects with and without the MS. CONCLUSIONS In non-stone formers, the risk of CaOx stone formation increases with the number of features of the MS. However, in stone-forming subjects, the propensity for CaOx precipitation is much higher but is not independently associated with increasing features of the MS.