Bone mass as referent for urinary hydroxyproline excretion: age and sex-related changes in 125 normals and in primary hyperparathyroidism.

Fasting urinary hydroxyproline: creatinine ratio (OHPr:Cr) and bone mineral content of the forearm (BMC) were measured in 125 normals, 67 females and 58 males, aged 20-79 years, and in 15 patients with primary hyperparathyroidism. In normals, both variables were significantly correlated to age and sex. The interrelation of OHPr:Cr and BMC was studied in subgroups of normals who were supposedly in metabolic balance, that is, females aged 20-39 years (n = 24) and males aged 20-49 years (n = 29). In both sexes OHPr:Cr and BMC were positively correlated: r = 0.60 and 0.58, respectively (P less than 0.001). On this basis, BMC correction of all OHPr:Cr values was undertaken now revealing a stable increased level of bone resorption per unit of bone mass in postmenopausal females. In males OHPr:Cr per unit of BMC remained unaltered throughout life. In primary hyperparathyroidism, in which increased bone resorption is inherent, the discriminatory power of OHPr:Cr was significantly improved when calculated per unit of BMC (P less than 0.001). These observations suggest that estimation of bone resorption by use of OHPr:Cr requires adjustment for differences in bone mass.