Urinary N-Telopeptide

NTX is a cross-linker for mature type I collagen that is specific to bone and is released into the circulation during the process of bone resorption. It is excreted unmetabolized in urine, making it a sensitive and specific marker of bone resorption during osteoporosis [16]. NTX was measured using an enzyme-linked immunosorbent assay (ELISA) using an Osteomark^® kit (Alere Inc., Waltham, MA, USA) one day before surgery. For normalization, creatinine (Cre) was measured using the second morning void urine samples as a baseline before surgery. The precision was calculated as the coefficient of variation (% CV: 3.8%) in this series. According to the guidelines of the Japanese Osteoporosis Society, the reference ranges for Cre-normalized urinary NTX have been established using a commercially available enzyme immunoassay as: 9.3 to 54.3 nmol bone collagen equivalent (BCE)/nmol•Cre in premenopausal females, 14.3 to 89.0 nmol BCE/nmol•Cre in postmenopausal females, and 13.0 to 66.2 nmol BCE/nmol•Cre in males [17]. In addition, NTX values can suggest bone diseases (>54.3), metastatic bone tumor (>89.0), or abnormal calcium metabolism (>66.2 nmol BCE/nmol•Cre). Finally, the cutoff level of NTX that indicates high risk of fracture is 54.3 nmol BCE/nmol•Cre [17].