Calcitriol load test in postmenopausal osteoporosis: a pilot study

Calcium and vitamin D balance is of critical importance in both, prevention and treatment of osteoporosis. The evaluation of this balance is difficult under steady state conditions, therefore the effect of a single oral calcitriol load in postmenopausal women with osteopenia/osteoporosis was used.

Mineral and hormone concentrations were determined under basal conditions and after the administration of a single 0.5 microg calcitriol dose (Rocaltrol, Roche).

Single oral calcitriol dose was administered to 36 postmenopausal women. Increased calciuria (p < 0.001) and calcium fractional excretion (p < 0.001) 24 hours after drug administration indicated kidney participation in calcium homeostasis. Urinary calcium excretion after the calcitriol load correlated with basal urinary calcium excretion (r = 0.772; p < 0.001). On the basis of calciuric response, women could be separated to responders and non-responders; in responders, increase in calciuria was >1.0 mmol/d, while in non-responders < 1.0 mmol/d (p < 0.001). Neither plasma calcium nor plasma 25-hydroxycholecalciferol concentrations increased after the calcitriol load. Both basal (r = -0.361; p < 0.03) and calcitriol stimulated urinary calcium excretion correlated inversely with age (r = -0.425; p < 0.01). No significant changes in measured mineral and hormone parameters were found in women with osteopenia in comparison to women with osteoporosis, with the exception of plasma intact parathormone concentration, which was significantly higher in osteoporotic women (p < 0.05) and significantly decreased (p < 0.001) after the calcitriol load.

Postmenopausal women suffered from calcium and vitamin D imbalance which could be elucidated by a simple calcitriol test. The reference range, significance and differentiation from other abnormalities are to be defined in an extensive study. (Tab. 4, Ref. 19.).