Clinical evaluation of the elecsys beta-CrossLaps serum assay, a new assayfor degradation products of type I collagen C-telopeptides

Background: The Elecsys beta -CrossLaps serum assay measures type I collage n degradation fragments (beta -CTx) that contain the beta -isomerized octap eptide EKAHD-beta -GGR. We investigated the analytical performance of the a ssay and changes in beta -CrossLaps in patients with metabolic bone disease s. Methods: The electrochemiluminescent sandwich immunoassay uses two monoclon al antibodies directed against different regions of the linear EKAHD-beta - GGR. Results: beta -CrossLaps (beta -CTx) immunoreactivity was stable in serum a nd plasma stored at 4 degreesC for 24 h or at room temperature for 4 h, and it did not decrease appreciably in samples stored at -30 degreesC for 12 w eeks. Nine cycles of repeated freezing-thawing did not affect serum beta -C Tx. The intra- and interassay imprecision (CVs) for four samples was less t han or equal to2.6% (n = 10) and less than or equal to4.1% (n = 10), respec tively. The mean day-to-day biological variation (CV) was 20% in 10 postmen opausal women (n = 10 days). Serum beta -CTx and osteocalcin were correlate d in patients with hyperparathyroidism (r = 0.796; P <0.0001; n = 28), chro nic renal failure on hemodialysis (r = 0.784; P = 0.0003; n = 16), hypopara thyroidism (r = 0.950; P = 0.0001; n = 11), and pseudohypoparathyroidism (r = 0.987; P = 0.130; n = 4). Serum beta -CTx decreased by 47.4% +/- 8.8% (m ean +/- SD) and 60.7% +/- 6.5% at 3 and 6 months, respectively, after initi ation of estrogen replacement therapy in 34 women. These decreases were gre ater than the decreases in urinary excretion of deoxypyridinoline (31.8% +/ - 3.9% and 38.1% +/- 4.4%, respectively) or pyridinoline crosslinked C-term inal telopeptide of type I collagen (15.9% +/- 3.9% and 16.9% +/- 4.6%, res pectively). Conclusions: The Elecsys beta -CrossLaps serum assay provides a potentially useful tool for assessing bone resorption state, including its response to estrogen replacement therapy. (C) 2001 American Association for Clinical C hemistry.