AUTOMATED AND MANUAL ASSAYS FOR URINARY CROSS-LINKS OF COLLAGEN - WHICH ASSAY TO USE

With the increasing demand for clinically useful biomarkers of bone tu rnover, a number of assays for the measurement of bone resorption mark ers have been developed. In the present study, automated (ACS:180 DPD, Chiron Diagnostics, USA) and manual (DPD-ELISA, Pyrilinks-D(TM), Metr a Biosystems, USA) immunoassays for free DPD, and a manual immunoassay for the aminoterminal telopeptide of type I collagen (NTX, Osteomark( TM), Ostex International, USA) were compared to the automated HPLC met hod for free DPD. Urine samples from a total of 538 healthy and diseas ed subjects aged 20 to 80 years were analysed. The age and sex stratif ied reference ranges were essentially identical for the HPLC, ACS:180 and the DPD-ELISA, but differed from the NTX assay. Individual values for free DPD as generated by HPLC and immunoassay techniques were high ly correlated with each other, whereas correlations between assays mea suring free and peptide-bound crosslink components were less pronounce d. Precision of the automated techniques (HPLC and ACS:180) was superi or to that of the manual immunoassays. Disease-specific changes in cro sslink excretion were similar for all assays and most pronounced in me tastatic osteopathy, primary hyperparathyroidism and untreated Paget's disease of bone. We conclude that the automated assays for free DPD i n urine, i.e. the HPLC and the ACS:180 assay, show better analytical p erformance than the manual immunoassays studied. All techniques used i n the present study appear to provide similar or identical clinical in formation. Therefore, the decision which assay to use largely depends on the laboratory set-up, the number of samples to be analysed, the tu rn-around time required, and the application for which the test should be used.