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NTx Telopeptide

Bone remodeling allows for bone growth, bone repair and elimination of microfractures. Osteoclasts resorb old bone, while osteoblasts synthesize new protein, known as osteoid. Within several months, osteoid becomes calcified. After the age of 40 years, bone destruction begins to exceed formation, leading to osteoporosis. For every 10% of bone that is lost, the risk of fracture doubles.

The medications most commonly used to treat osteoporosis are estrogen, calcitonin and biphosphonates (etidronate, alendronate, risedronate). Their mechanism of action is to inhibit osteoclastic activity and decrease bone resorption. Treatment with biphosphonates must be continuously monitored because overdosage can eventually weaken bone.

More than 90% of the osteoid matrix of bone consists of type I collagen. Noncollagenous proteins, such as osteocalcin, comprise the remaining 10%. Type 1 collagen is synthesized as procollagen precursor molecules. Prior to insertion into the osteoid matrix, the N and C terminal peptides of procollagen are cleaved and released into the circulation. The N terminal peptide is commonly referred to as N-telopeptide and is one of the most sensitive indicators of bone resorption.

Following initiation of treatment, bone resorption markers can detect early changes much sooner than bone mass density measurements. N-telopeptide levels undergo significant change by 3 months, while changes in spinal bone mass density are noticeable only after 24 months.

A baseline N-telopeptide level should be measured in all patients before beginning anti-resorptive therapy. In general, biphosphonates are administered until N-telopeptide levels fall to 50% of baseline. They are then discontinued and N-telopeptide concentration is measured every 3 months. Treatment is reinstated when the level returns to baseline.

Reference range is 5.4-24.2 nM BCE for adult males and 6.2-19.0 nM BCE for premenopausal women. Results are expressed in bone collage equivalents (BCE).

Specimen requirement is a red top tube of blood.

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