N-Telopeptide Cross-links (NTx), Urine

Urine

20 mL

1 mL

Plastic urine container without preservative

Evaluation of osteoporosis and assessment of antiresorptive therapy

Ortho Vitros Enhanced Chemiluminescence System

• Pediatric: see table.¹

• Adults:

− Male: 0−62 nM BCE/mmol creatinine

− Female: 20 to 49 years 0−64 nM BCE/mmol creatinine; >49 years 0−89 nM BCE/mmol creatinine

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.¹ 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. Osteoporosis occurs when there is an imbalance between bone formation and bone resorption leading to net bone loss.^2-5 Certain aspects of this bone composition and structure that contribute to increased bone fragility may not be captured by bone mineral density measurements.⁵

Bone resorption by osteoclasts results in the production of cross-linked N-telopeptides of type I collagen (NTx).¹ NTx is specific to bone and is found in urine as a stable end product of bone degradation. 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.^2-8 Osteoporotic fractures are a major source of morbidity and mortality in older women.² 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 therapy⁷ 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 study⁸ supported the use of NTx to identify the probability of a decrease in bone mineral density after one year in postmenopausal women receiving a calcium supplement relative to those treated with hormonal antiresorptive therapy.

Several studies have shown that certain biochemical markers of bone turnover, measured in serum or urine, can be used as independent predictors of fractures, especially spine and hip.^2,6 Bone mineral density (BMD) is often used to monitor the efficacy of osteoporosis treatment and to follow patient compliance. Unfortunately, changes in BMD in response to treatment are slow, and it takes at least one year of treatment before a significant change in BMD can be observed in many cases.^2,7 As a result, the absence of BMD increase does not necessarily indicate a lack of therapeutic response.^2,7 The use NTx can be helpful for assessing early changes in BMD (baseline vs post-treatment) revealing a biological effect of the medication and proving patient compliance and persistence.^2,7