THE DIAGNOSTIC VALIDITY OF URINARY FREE PYRIDINOLINES TO IDENTIFY WOMEN AT RISK OF OSTEOPOROSIS

The urinary excretion of pyridinolines either in the free form or link ed to different peptide fragments of type I collagen are intensively s tudied as new biochemical markers of bone resorption. In the present s tudy we compared the urinary excretion of free pyridinoline (F-Pyr) de termined by enzyme-linked immunosorbent assay (ELISA) (Collagen Crossl inksTM Kit, Metra Biosystems) to pyridinoline (Pyr), and deoxypyridino line (D-Pyr) determined by high performance liquid chromatography (HPL C) in early postmenopausal women treated with either hormone replaceme nt therapy or placebo and in healthy age-matched premenopausal women. Other markers of bone metabolism were included for comparison. Compare d with the premenopausal women, the postmenopausal women had significa ntly increased values of the biochemical parameters. F-Pyr, Pyr, D-Pyr , and T-Pyr(= Pyr + D-Pyr) decreased during hormone therapy. D-Pyr cor related with the rate of bone loss, whereas this was not the case for F-Pyr. The correlations between the markers yielded r values of 0.71 ( F-Pyr vs Pyr), 0.67 (F-Pyr vs D-Pyr), and 0.71 (F-Pyr vs T-Pyr). In co nclusion, the present study shows that the newly introduced ELISA for determination of the free pyridinolines is less sensitive than pyridin ium crosslinks measured by high performance liquid chromatography (HPL C) in hydrolyzed urine for the changes in calcium metabolism that occu r at menopause and during hormone replacement therapy. Whether this li mitation will be balanced out by avoiding the inconvenience of the com plicated, expensive, and time-consuming HPLC procedure is still being debated.