[Urinary calcium and bone turnover markers]

To know the relationship between bone turnover markers and urinary calcium excretion with and without oral calcium load in postmenopausal and young women.

A cross-sectional study in 100 women (50 with normal menstrual cycle and 50 postmenopausal). After 5 days with a specific diet, urine of 24 hours, 2 hours in fasting, and 4 hours after oral calcium load was collected (the last urine collection was only done in 20 patients in each group. In these patients, an x-ray absorptiometry of distal forearm and vitamin D levels were evaluated too). Calcium, alkaline phosphatase, calcitonin, parathormone, N-telopeptides of type I collagen, and osteocalcin serum levels were measured in fasting. Creatinine and calcium were measured in urine to obtain the Ca/cr index.

Postmenopausal women had lower calcitonin levels while the Ca/cr index of 2 hours in fasting was higher than the eumenoreic women. We found significant correlation between Ca/cr index of 2 hours with age (R = .21; p = .04), parathormone (R = .21; p = .04), and calcitonin levels (R = -.29; p = .005). There was not correlation with the urinary calcium excretion including the 4 hour postload collection with the biochemical markers of bone turnover or mineral bone density of distal forearm.

The urinary Ca/Cr index of 2 hours in fasting is related to parathormone levels and has a negative relationship with calcitonin levels in postmenopausal women. However, the urinary calcium excretion after oral calcium load was not related with the bone turnover grade.