Biological Variation in Serum Type I Collagen Carboxy-Terminal Telopeptide Concentrations

Roche Diagnostics recently automated (1) (on the Elecsys® analyzer) the β-CrossLapsTM assay (2) for measurement of bone-derived degradation products of type I collagen carboxy-telopeptide in serum (s-βCTX). However, information on the biological variation of s-βCTX is lacking, a fact that is limiting because the clinical utility of bone markers can be significantly affected by their physiological variations (3). To investigate the biological variation of s-βCTX, we took four blood specimens from each of 10 healthy volunteers (5 men and 5 premenopausal women; ages 25–50 years) on the same day once a week for 4 weeks. “Healthy” subjects were studied to ensure that any fluctuation in s-βCTX concentrations could truly be attributed to biological variation and were not caused by pathological variations in bone homeostasis. In accordance with the Helsinki II Declaration, the design and execution of the experiment were explained thoroughly to the subjects, and informed consent was obtained. The inclusion criteria were that the subjects be within 20% of ideal body weight, have no bone or connective tissue disorder, and for women, have regular menstrual cycles and no use of hormonal contraceptives. In addition, none of the subjects took any medication or consumed substantial quantities of alcohol.