Coated-tube radioimmunoassay for C-telopeptides of type I collagen to assess bone resorption.

We present a coated-tube RIA that is useful for assessment of bone resorption. The assay uses a monoclonal antibody raised against a linear 8-amino-acid sequence (EKAHDGGR) derived from the C-telopeptides of type I collagen. Within-run and total CVs were 4.4% and 5.3-6.2%, respectively, at concentrations of 1-7 mg/L (n = 4-20). Analytical recovery was 98% +/- 8% and dilution 97% +/- 7%. Values obtained in a group of 36 premenopausal women were 227 +/- 89.6 mg/mol creatinine. In a group of 141 postmenopausal women, the values obtained were 429 +/- 225 mg/mol creatinine, a highly significant increase of 89% (P <0.001) over the premenopausal value. In a double-blind placebo-controlled clinical study of these postmenopausal women receiving five different doses of a bisphosphonate, a significant decrease of RIA-measured C-telopeptide values was seen in all bisphosphonate-treated groups, after just 3 months. Values in urine samples from postmenopausal women assayed with the RIA (gamma) and the CrossLaps(TM) ELISA (x) agreed well: slope = 0.98 (95% confidence interval, 0.94-1.01), intercept = 0.34 (0.25-0.43) mg/L, and Sylx = 0.93 mg/L (n = 678). We conclude that this RIA represents a valuable tool for assessing bone resorption.