Endocrine Abstracts

In contrast to bone formation biomarkers, reliable bone resorption biomarkers have not been available in serum. Recently, automated measurement of C-terminal cross-linking telopeptide of type I collagen (CTX-I), has been promoted as a reliable indicator of bone resorption. The objective of the study was to examine the correlation of CTX-I, with the traditional urinary markers, N-telopeptide of type I collagen (NTX-I) and deoxypyridinoline (DPD) in a series of patients with Paget's disease (n=26), osteoporosis (n=18), osteogenesis imperfecta (n=8), patients with adrenal insufficiency receiving glucocorticoid treatment (n=34) and other groups (n=9).

Biochemical markers of bone turnover are highly susceptible to biological, pre-analytical and analytical variability. To minimise circadian inconsistencies, serum with simultaneous early morning two-hour timed urine samples were collected from 95 fasting subjects. Samples were separated and frozen within 30 minutes of collection and stored at -30 degrees celcius prior to analysis. Serum

CTX-I was analysed using a novel electro-chemiluminescent technique utilising two monoclonal antibodies specific for crosslinked isomerised type I collagen fragments. NTX-I and DPD were assayed using enzyme linked immunosorbent assays.

Results: Serum CTX-I correlated positively with NTX-I r = 0.85; p<0.0001 and with DPD r = 0.58; p <0.0001. The urinary resorption markers NTX-I and DPD also correlated positively, r = 0.82; p<0.0001. These results suggest that serum CTX-I and urinary NTX-I provide equivalent information on bone resorption status in fasting early morning samples. While more extensive evaluation is warranted these results suggest that measurement of CTX-I in serum provides a valuable indicator of bone resorption.