Bone resorption and hypercalciuria in calcium stoneformers

The circadian rhythm of urinary total hydroxyproline (THP) excretion was determined in matched groups of ten male idiopathic calcium stoneformers and ten normal subjects in order to determine whether enhanced resorption of bone might contribute to hypercalciuria in these patients. THP increased progressively in normal subjects in successive eight-hour urine collections from period 1 (8 AM to 4 PM) to period 3 (12 midnight to 8 AM), the nocturnal high level in period 3 being significantly greater than in period 1 (P less than 0.01) and in period 2 (P less than 0.05). By contrast, no significant circadian rhythm was observed in THP excretion in the stoneformers. Their THP excretion was similar to that of normal subjects in period 3, but was significantly higher than that of normal subjects in period 1 (THP/creatinine ratio(mg/mg): 0.026 +/- 0.003 v 0.017 +/- 0.001; P less than 0.05. Indices of parathyroid hormone activity were not significantly different between stoneformers and normal subjects; mean serum 1,25(OH)2 vitamin D levels were higher in the stoneformers than the normal subjects (44 v 37 pg/mL) but the difference was not significant (P greater than 0.05). These studies suggest that increased bone turnover may contribute to hypercalciuria in these calcium stoneformers.