EFFECT OF URINARY CALCIUM EXCRETION ON BONE MARKERS IN OSTEOPOROTIC PATIENTS

Abstract

Background: Urine calcium excretion (UCaE) could reflect calcium balance and bone activities. High UCaE is prevalent among patients with osteoporosis. However, the relationship between UCaE and bone turnover markers is not well-studied.

Methods: Cross-sectional study of post-menopausal women with refractory osteoporosis. Total and ionized calcium, UCaE, estimated GFR, PTH including cyclase activating PTH (CAP); and cyclase inhibitory PTH (CIP), markers of bone formation, osteocalcin and bone-specific alkaline phosphatase (BSAP), and bone resorption, serum N-telopeptide Collagen (NTX) were recorded.

Results: Study included 205 post-menopausal women with mean age of 64±10 years. HTN was found in 36%, while DM in 6%, and 13% of patients had CKD. Kidney stones were recorded in 7%, while 77% of patients had previous fractures. Only 4% of patients had vitamin D deficiency. Serum calcium and phosphorus correlated positively with osteocalcin, while ionized calcium correlated also with NTX. Alkaline phosphatase showed a positive correlation with bone formation markers. Estimated GFR correlated negatively with age, phosphorus, PTH CIP, and NTX, while it correlated positively with UCaE. Urinary calcium did not correlate with bone formation or resorption markers, but it correlated negatively with iPTH and PTH CAP. Urine calcium/creatinine ratio correlated positively with vitamin D levels.

Conclusion: In post-menopausal women with refractory osteoporosis, patients with mild renal impairment had higher phosphorus, PTH CIP, and NTX levels and lower urinary calcium. Apart from negative correlation with iPTH and PTH CAP, UCaE did not correlate with bone formation or resorption markers. Higher vitamin D levels were associated with increased urinary calcium/creatinine ratio.