Serum Concentrations of Cross-Linked N-Telopeptides of Type I Collagen: New Marker for Bone Resorption in Hemodialysis Patients (Endocrinology and Metabolism‪)‬

Renal osteodystrophy is one of the major complications in hemodialysis (HD) [3] patients, leading to a substantial increase in fracture rate and increased morbidity and mortality (1). Bone mineral density (BMD) is widely used to estimate bone fracture risk. In addition, evaluation of bone turnover rate is established as an independent predictor for bone fracture (2, 3) and future bone loss (4), and measurements of bone metabolic markers are increasingly used to complement BMD measurements (5, 6). Bone resorption markers are assumed to be superior to bone formation markers for predicting future changes in bone mass, well in advance of detection of BMD reductions (7). Measurement of cross-linked N-telopeptide of type I collagen (NTX) in serum was recently approved in Japan for clinical use as a bone resorption marker. Impaired urinary excretion precludes urinary measurement of bone resorption markers in HD patients, but measurement of serum NTX may provide a good marker for the bone resorption state in these patients. We recently reported (8) that the (3-CrossLaps assay for serum Cterminal telopeptide of type I collagen ([beta]-CTX) (9-11) provides values that are no less significant than those for pyridinoline (PYD) and deoxypyridinoline (DPD), 2 commonly used serum bone resorption markers, in assessing bone metabolism in HD patients. Because NTX is derived from a different part of the same type I collagen as ([beta]-CTX (the N[H.sup.2] and COOH termini for NTX and ([beta]-CTX, respectively), it is important to determine the significance of serum NTX as a bone resorption marker in HD patients. We assessed the performance of serum NTX as a bone resorption marker in HD patients, compared with other established markers of bone resorption (([beta]-CTX, PYD, and DPD) and bone formation [bone alkaline phosphatase (BAP) and intact osteocalcin (OC)], by examining the correlation of NTX with other markers and with the rate of bone loss over a subsequent 2-year period.