Immunoassay for urinary pyridinoline: the new marker of bone resorption

Urinary pyridinoline (Pyd) and deoxypyridinoline (Dpd) are markers of bone resorption that are elevated above normal in subjects with metabolic bone disease. Total Pyd and Dpd, both free and peptide-bound forms, can be measured by HPLC after hydrolysis and cellulose chromatography. Since free Pyd is the major component of total Pyd in urine, we developed an immunoassay using free Pyd as an immunogen. This assay is much easier to perform than HPLC, requires no sample preparation, and correlates well with total Pyd measurement by HPLC (r = 0.97) and with urinary hydroxyproline (r = 0.90). The antiserum reacts most strongly with free Pyd and Dpd and minimally with glycosylated and large peptide-bound forms. The sensitivity of the Pyd immunoassay is less than 25 nM. The intraassay CV is 5-10%; the interassay CV is 10-15%. Analytic recovery studies indicated negligible sample interference. Furthermore, measurement of the Pyd in the same individuals over a 30 day time period exhibited minimal day-to-day variation. Thus, the Pyd immunoassay provides a rapid and easy method for evaluation of Pyd in urine. Pyd immunoassay may serve as a practical method of screening for metabolic bone disease and for monitoring therapeutic treatment.