Test Catalog

Test ID: SNTX    
N-terminal Telopeptide, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Monitoring effectiveness of antiresorptive therapy in patients treated for osteoporosis or other metabolic bone disorders


As an adjunct in the diagnosis of medical conditions associated with increased bone turnover


This test is not useful for screening or diagnosing osteoporosis.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Human bone is continuously remodeled through the process of bone formation and resorption. Measurement of bone turnover markers (BTM) in serum or urine serves as an indicator of bone formation or bone resorption cellular activities. BTM are physiologically elevated during childhood, growth, and during fracture healing. The elevations in bone resorption markers and bone formation markers are typically balanced in these circumstances and of no diagnostic value. Bone diseases occur when formation and resorption are uncoupled. In these situations, BTM might serve as predictors of therapy response.


Telopeptides of type 1 collagen are the most extensively studied and used bone resorption markers. There are 2 forms depending on the cross-link forming site with collagen: the N-terminal telopeptide (NTx) and C-terminal telopeptide (CTx), which are released during collagen degradation.


In osteoporosis, a disease characterized by low bone mass and deterioration of bone tissue leading to increase skeletal fragility, measurement of BTM helps to determine treatment efficacy or patient's compliance with therapy. The advantage of measurement of BTM is that changes in response to therapy are observed within 3 to 6 months after therapy initiation; whereas changes in bone mineral density are not observed until 12 to 24 months posttherapy. Other diseases affecting the bone remodeling process, such as hyperthyroidism, all forms of hyperparathyroidism, most forms of osteomalacia and rickets (even if not associated with hyperparathyroidism), hypercalcemia of malignancy, Paget disease, multiple myeloma, bony metastases, as well as various congenital diseases of bone formation and remodeling, can result in accelerated and unbalanced bone turnover and elevation of BTM.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

All units are reported in nmol bone collagen equivalents (BCE)

Adult (> or =18 years of age)



5.4-24.2 nmol BCE



Premenopausal: 6.2-19.0 nmol BCE

The target value for postmenopausal adult females undergoing treatment for osteoporosis is the same as the premenopausal reference interval.

Interpretation Provides information to assist in interpretation of the test results

Elevated levels of N-terminal telopeptide (NTx) indicate increased bone resorption.


A 30% or greater reduction in this resorption marker 3 to 6 months after initiation of therapy indicates a probably adequate therapeutic response.


A common target of antiresorptive therapy in the treatment of postmenopausal osteoporosis is to achieve bone markers concentrations within the premenopausal reference range.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Serum N-terminal telopeptide (NTx) should not be used for the screening or diagnosis of osteoporosis. In patients with other clinical conditions known to affect bone resorption (eg; cancer metastases to bone), interpretation of serum NTx for monitoring response to osteoporosis therapy might be unreliable.


Do not interchange the Osteomark NTx serum assay values with the Osteomark NTx urine assay values, especially when monitoring therapy.


Some patients who have been exposed to animal antigens, either in the environment or as part of treatment or imaging procedures, may have circulating anti-animal antibodies present. These antibodies may interfere with the assay reagents to produce unreliable results.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Lee J, Vasikaran S: Current recommendations for laboratory testing and use of bone turnover markers in management of osteoporosis. Ann Lab Med. 2012 Mar;32(2):105-112

2. Chopin F, Biver E, Funck-Brentano T, et al: Prognostic interest of bone turnover markers in the management of postmenopausal osteoporosis. Joint Bone Spine. 2012 Jan;79(1):26-31

3. Hlaing TT, Compston JE: Biochemical markers of bone turnover-uses and limitations. Ann Clin Biochem. 2014 Mar;51(Pt 2):189-202