Consistency of Bone Turnover Marker and Calcium Responses to Parathyroid Hormone (1-84) Therapy in Postmenopausal Osteoporosis

We investigated whether those who experience the greatest increases in bone turnover in response to parathyroid hormone (PTH) therapy are the same as those who experience elevations in calcium levels. Baseline and follow-up procollagen type I N propeptide (PINP), bone-specific alkaline phosphatase (BAP), C-terminal telopeptide (CTX), and serum and urinary calcium levels were analyzed post hoc from the 119 postmenopausal women with osteoporosis randomized to PTH(1-84) in the Parathyroid Hormone and Alendronate trial. Short-term changes in the markers of bone turnover were highly correlated with one another (r = 0.57-0.87, p < 0.001). In contrast, change in serum calcium correlated only modestly with changes in markers of formation (r = 0.22-0.30, p ≤ 0.02) and did not correlate significantly with change in CTX (r = 0.13, p = 0.18). Participants who experienced hypercalcemia experienced greater 3-mo changes in BAP than those who did not (78% vs. 42% increase in BAP, p = 0.04), with similar trends for PINP and CTX. In conclusion, the use of 1 marker of bone turnover, rather than multiple markers, may be sufficient to assess biochemical response to PTH(1-84). The relationship between bone turnover marker and calcium responses to PTH(1-84) is modest and does not suggest a profound, broadly heightened responsiveness of certain individuals to therapy.