Validation of a high-performance liquid chromatographic assay for lysylpyridinoline in urine: A potential biomarker of bone resorption

We developed and validated a high-performance liquid chromatographic (HPLC) method for quantifying the bone-specific collagen crosslink, lysylpyridinoline (LP), in urine. LP was purified from cortical bone and characterized by spectrophotometry, HPLC, and H-1 NMR spectroscopy. Our HPLC detected urinary LP independently of the sample volume and the range of quantification was between 63 nM and 1 mu M. Average recovery of added LP standard to human urine samples was 106 +/- 21%. Mean inter- and intraassay CVs, respectively, for urines containing low, medium, and high concentrations of the crosslink LP were 7.4 and 6.3%. This analytical method is more efficient than previously published HPLC assays for LP because of the significant 24-h reduction in urinary sample preparation time. There was agreement between urinary LP concentrations measured with this method and the Metra Pyrilinks-D enzyme immunoassay (r(2) = 0.714). These results emphasize the importance of using a thoroughly standardized HPLC assay as the ''gold standard'' for comparison of results with newly developed immunoassays. (C) 1996 Academic Press, Inc.