Calcium-binding proteins and renal lithiasis.

The present study consists of measuring calcium-binding activity in urine obtained from 17 metabolically active noninfectious calcium oxalate stone formers, six inactive calcium oxalate stone formers, two active uric acid stone formers, one active cystine stone former, and seven nonstone-forming controls. Twenty-four hour specimens were obtained from each patient and were ultrafiltered, utilizing a series of membranes to concentrate all macromolecules of molecular weight less than 50,000 daltons. The concentrated specimen was separated by gel filtration chromatography, and each fraction was analyzed for calcium-binding activity utilizing the chelex resin binding assay. Total urinary calcium binding protein activity was significantly greater in the active calcium oxalate stone formers when compared with either inactive calcium oxalate stone formers (P less than 0.025) or nonstone-forming controls (P less than 0.05). The number of uric acid and cystine stone formers was too small to make meaningful comparisons. Urinary excretion of calcium binding appears to be related to stone activity and may be specific for calcium stone formers. Their influence on stone formation deserves further study.