Calcium metabolism and osteoporosis in corticosteroid-treated postmenopausal women.

Osteoporosis is a common complication of corticosteroid therapy and it is associated with both decreased bone formation and increased bone resorption. We have measured radiocalcium absorption and the fasting urinary calcium/creatinine and hydroxyproline/creatinine ratios in 30 postmenopausal women receiving prednisolone therapy and compared the patients with normal spine radiographs (N = 14) with those whose spine radiographs showed osteoporosis (N = 16). The osteoporotic cases had lower radiocalcium absorption (p less than 0.001), higher fasting urinary calcium (p less than 0.05), and higher fasting urinary hydroxyproline excretion (p less than 0.001). As calcium absorption has a positive effect on calcium balance and urinary calcium a negative effect, the difference between these two variables was calculated in each case. This derived variable (radiocalcium absorption--fasting urinary calcium/creatinine) disclosed a greater difference between the osteoporotic and normal groups (p less than 0.0001) than either variable alone.