Biological or Clinical Significance:
Bone resorption is a function of osteoclasts. These cells remove the mineral from bone and break down the organic matrix, which is primarily comprised of type I collagen. Collagen is a cross-linked fibrous protein that forms the fabric of bone and most other connective tissues. Bone contains three polypeptides chains wound together in a helical structure. The ends of these chains (known as telopeptides) provide the intermolecular cross-linking that gives collagen its strength and resiliency. As these cross-linked domains from bone and other skeletal connective tissues are broken down, the pyridinoline cross-linking domains are released and enter the bloodstream. One type of peptide-bound pyridinoline is the cross-linked N-telopeptide (NTx) which is unique to type I bone collagen. NTx can be used to identify fast losers of bone, to monitor therapy, to measure dose response, or to determine compliance.
Principle of Test Method:
The NTx assay is a solid-phase ELISA that employs the quantitative competitive enzyme immunoassay principle.
Gertz, BJ, Clemens, JD, Holland, SD, Yuan, W, and Greenspan, S. Application of a new serum assay for type I collagen cross-linked N-telopeptides: Assessment of diurnal changes in bone turnover with and without alendronate treatment. Calcif Tissue Int. 1998; 63:102-106.
Ali SM, Demers LM, Leitzel K, Harvey HA, Clemens D, Mallinak N, Engle L, Chinchilli V, Costa L, Brady C, Seaman J, Lipton A. Baseline serum NTX levels are prognostic in metastatic breast cancer patients with bone-only metastasis. Ann Oncol. 2004; 15:455-459.