Bone is continuously remodeled through a process of osteoclast-mediated bone formation and resorption. This process can be monitored by measuring urine markers of bone formation and resorption known as N-Telopeptides (NTx). Unbalanced bone turnover is found in age-related and postmenopausal osteopaenia and osteoporosis.
Approximately 90% of the organic matrix of bone is type I collagen, a helical protein that is cross-linked at the N- and C-terminal ends of the molecule. The amino acid sequences and orientation of the cross-linked alpha 2 N-telopeptide of type 1 collagen make it a specific marker of human bone resorption. N-terminal telopeptide (NTx) molecules are mobilised from bone by osteoclasts and subsequently excreted in the urine. Elevated levels of NTx indicate increased bone resorption.
Bone turnover markers are physiologically elevated during childhood, growth and during fracture healing. The elevations in bone resorption markers and bone formation markers are typically balanced in these circumstances and of no diagnostic value. By contrast, abnormalities in the process of bone remodelling can result in changes in skeletal mass and shape. Many diseases, in particular hyperthyroidism, all forms of hyperparathyroidism, most forms of osteomalacia and rickets (even if not associated with hyperparathyroidism), hypercalcaemia of malignancy, Paget’s disease, multiple myeloma and bony metastases, as well as various congenital diseases of bone formation and remodelling can result in accelerated and unbalanced bone turnover.
Common Conditions:
- Osteoporosis
- Chronic bone/muscle/joint pain
- Menopause
References:
Dmowski WP, Rana N, Pepping P, Cain DF, Clay TH. Excretion of urinary N-telopeptides reflects changes in bone turnover during ovarian suppression and indicates individually variable estradiol threshold for bone loss. Fertil Steril. 1996;66(6):929‐936. doi:10.1016/s0015-0282(16)58685-3
Ulrich U, Rhiem K, Schmolling J, et al. Cross-linked type I collagen C- and N-telopeptides in women with bone metastases from breast cancer. Arch Gynecol Obstet. 2001;264(4):186‐190. doi:10.1007/s004040000105
