Collagen Cross-Linked N-Telopeptide (NTx), Urine
Approximately 90% of the organic matrix of mammalian bone consists of type I collagen that is cross-linked at the N-terminal and C-terminal ends. This highly cross-linked structure provides for the basic fabric and tensile strength of bone tissue. The collagen infrastructure of bone undergoes a continuous process of remodeling that involves osteoclast-mediated bone resorption and osteoblast-mediated bone formation. Bone resorption by osteoclasts results in the production of cross-linked N-telopeptides of type I collagen (NTx). NTx is specific to bone and is found in urine as a stable end product of bone degradation.
The NTx test measures the concentration of cross-linked N-telopeptides of type I collagen. Levels of NTx correlate with the rate of bone resorption. Bone resorption rates exceeding bone formation results in a net loss of bone and ultimately osteopenia or osteoporosis. Osteoporotic fractures are a major source of morbidity and mortality in older women.
The NTx test is intended for use in predicting skeletal response to hormonal antiresorptive therapy in postmenopausal women. The NTx test can also be used to monitor the efficacy of antiresorptive therapy in postmenopausal women, women with osteoporosis, and individuals with Paget disease. The NTx test can also be used in monitoring the effect of estrogen-suppressing therapies on the rate of bone resorption. A recent study7 supported the use of NTx to identify the probability for a decrease in bone mineral density after one year in postmenopausal women receiving calcium supplement relative to those treated with hormonal antiresorptive therapy.
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