Assessment of bone remodeling using biochemical indicators of type I collagen synthesis and degradation: relation to calcium kinetics

In this study, we investigated the relation between calcium kinetic indices of bone remodeling (resorption rate, r; and formation rate, m, respectively) and two serum markers of type I collagen turnover: the pyridinoline cross-linked carboxyterminal telopeptide domains of type I collagen (S-ICTP a marker of bone matrix degradation) and the carboxyterminal propeptide of human type I procollagen (S-PICP, a marker of bone matrix formation). We studied three groups: (i) healthy controls (n = 19), (ii) a mixed group of high and low-turnover bone diseases without mineralization defects (myxedema, thyrotoxicosis and primary hyperparathyroidism n = 38), and (iii) osteoporosis (n = 52). In healthy controls, a significant regression of S-PICP on m was obtained (R = 0.53, SEE/Y = 0.44, P < 0.02). Significant regressions were also demonstrable in high- and low-turnover bone disease (R = 0.50, P < 0.001), SEE/Y = 61%) and osteoporosis (R = 0.49, P < 0.001, SEE/Y = 50%). In controls the regression coefficient for the regression of S-ICTP on r was 0.19 (NS), in high and low turnover bone disease 0.66, (SEE/Y = 59%, P < 0.001) and in the osteoporotic group 0.40 (SEE/Y = 61%, P < 0.01). We conclude that S-PICP and S-ICTP reflect whole skeletal bone formation and resorption rates in a variety of metabolic bone diseases including osteoporosis.