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Test Code NTX N-Telopeptide Cross-links (NTx), Serum

Reference Values

 Male: 5.4−24.2 nM BCE/L

• Female: 6.2−19.0 nM BCE/L


BCE = Bone Collagen Equivalent

Test Classification and CPT Coding


Physician Office Specimen Requirements

Container/Tube:  Gold top tube

Specimen: 0.5 mL serum ( 0.3 mL min-does not allow for repeat testing)

Transport Temperature: Refrigerated


Special Instructions

For monitoring therapy, baseline specimens should be collected just prior to or on the day of therapy initiation. Subsequent specimens for comparison should be collected at approximately the same time of day as the baseline specimen.


Used For

Monitor antiresorptive therapy with estrogen and calcium supplementation as well as drug therapy


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 serum and urine as a stable end product of bone degradation. Serum levels of NTx have been shown to correlate well with urine NTx normalized to creatinine. 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 result 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 level of serum NTx correlates with bone mineral density in elderly women. The serum NTx test can be used to monitor the efficacy of antiresorptive therapy with estrogen and calcium supplementation7 as well as drugs such as alendronate


Enzyme immunoassay (EIA)

Computer Interface Code

PDM #  5913275

Performing Laboratory