Urine pyridinium cross-links determinations by Beckman Cross Links Kit

Increased understanding of bone turnover has led to the development of several biochemical tests of bone metabolism. Among the biochemical indexes of bone resorption is measurement of urinary excretion of pyridinoline (Pyr) and deoxypyridinoline (Dpyr), molecules that cross-link the collagen chains and are released into the systemic circulation after the breakdown of mature bone collagen (1)(2)(3). Because they are not metabolized in vivo, they are excreted directly into urine in free (∼40%) and peptide-bound forms (∼60%) (4). Methods to measure cross-links in urine involve mainly two technical approaches: HPLC analysis, which, after hydrolytic and purification steps, allows the determination of the total forms of cross-links (5)(6)(7), and monoclonal antibody immunoassay methods able to quantify the sum of free Pyr and Dpyr or only the free Dpyr form (8)(9). The quantification of total or free cross-links forms provides, in any case, similar clinical information (9)(10). Here we report the evaluation of the Cross LinksTM HPLC kit recently introduced by Beckman Labs. to quantify the total forms of Pyr and Dpyr. We compared the performance of this procedure with the Chrom- LinksTM