This kit replaces the NTx-Serum (Osteomark®) N-Terminal Telopeptide of Type I Collagen kit (9021). These two kits are identical in raw materials used, manufacturing process, and QC parameters.

The ZEUS ELISA NTx Serum Test System is an immunoassay that provides a quantitative measurement of cross-linked N-telopeptides of type I collagen (NTx) in human serum.

Serum NTx levels can be used to:

  • Predict skeletal response (bone mineral density) to antiresorptive therapy
  • Monitor bone resorption changes following initiation of antiresorptive therapy.

Prior to initiating antiresorptive therapy, a serum NTx level is used to determine the probability for a decrease in bone mineral density (BMD) after one year in postmenopausal women treated with hormonal antiresorptive therapy relative to those treated with calcium supplementation.

This test is for in-vitro diagnostic use only.


Quick Facts

  • Range: 3.2-40 nM BCE
  • Sample Volume: 50 µl sample + 200 µl diluent
  • Sample Type: Serum



Bone is a dynamic and evolving tissue. Bone tissue undergoes constant bone turnover which involves the destruction of bone (bone resorption) followed by the construction of new bone (bone formation). In mammals, this continuous remodeling of bone is accomplished through a coupled process of osteoclast mediated bone resorption, followed by osteoblast mediated bone formation. This process is necessary for normal development and maintenance of the skeleton. When balanced, resorption and formation result in healthy bone tissue. If there should be an abnormal imbalance in these two processes, this may result in changes in skeletal mass and shape.

NTx is a collagen degradation product that functions as a marker of bone resorption. Approximately 90% of the organic matrix of bone tissue is type I collagen. NTx is generated from the amino terminus of the type 1 collagen by cleavage of the N-terminal region by cathepsin K during the resorption phase of bone turnover.

Bone turnover markers such as NTx have clinical utility in the comprehensive evaluation of osteoporosis. Elevated concentrations of NTx indicate elevated levels of bone resorption. When interpreted with caution and with a good understanding of its natural variability, measurement of NTx may provide information that supplements osteoporosis management and provide useful clinical information about the conditions that alter bone turnover.


Assay Principle

The ZEUS NTx Serum assay is a competitive-inhibition enzyme-linked immunosorbent assay (ELISA/EIA) for quantitative determination of NTx in human serum. NTx epitope is adsorbed onto a 96-well microplate. Diluted samples are added to the microplate wells, followed by a horseradish peroxidase labeled monoclonal antibody. NTx in the patient sample competes with the NTx epitope in the microplate well for antibody binding sites. Following a wash step, the amount of labeled antibody bound is measured by colorimetric generation of a peroxide substrate. Absorbance is determined spectrophotometrically and NTx concentration calculated using a standard calibration curve. Assay values are reported in nanomoles Bone Collagen Equivalents per liter (nM BCE).




A 1 Plate Antigen coated 96-microwell plate. 12 x 8-well strips coated with synthetic NTx antigen.
B 40 mL bottle Specimen Diluent. Buffered reagent into which calibrators, controls and specimens are diluted. ProClin™ 300 (0.05%) included as a preservative.
C 0.4 mL vial Antibody Conjugate Concentrate. Solution containing purified mSerum monoclonal antibody directed against NTx conjugated to horse radish peroxidase and Proclin™ 300 (0.1%). Supplied as a 100X concentrated conjugate.
D 25 mL bottle Antibody Conjugate Diluent. Buffered reagent with protein stabilizers, into which Antibody Conjugate Concentrate is diluted. ProClin™ 300 (0.05%) included as a preservative.
E 0.9 mL bottle Chromogen Reagent. One vial containing a solution of 3,3’,5,5’ – tetramethylbenzidine in dimethyl-sulfoxide. Supplied as a 100x concentrate.
F 30 mL bottle Buffered Substrate. One bottle containing a buffered hydrogen peroxide solution.
G 25 mL bottle Stopping Reagent. One bottle containing a solution of 1N sulfuric acid.
H 125 mL bottle 30X Wash Buffer Solution. One bottle containing a 30X ionic detergent solution.
0 0.4 mL vial 0 nM BCE Calibrator
5 0.4 mL vial 5 nM BCE Calibrator
10 0.4 mL vial 10 nM BCE Calibrator Various amounts of purified NTx antigen in stabilized protein diluent.
20 0.4 mL vial 20 nM BCE Calibrator Contains ProClin™ 300 (0.05%) as a preservative.
40 0.4 mL vial 40 nM BCE Calibrator
I 0.4 mL vial Level I Serum Control Human serum material with known NTx concentration. ProClin™ 300 (0.10%) included as a preservative.
II 0.4 mL vial Level II Serum Control
Plate Sealers 1 pad

Measurement range:

3.2 to 40 nM Bone Collagen Equivalents (BCE).


Expected Values:

Category n= Average NTx

(nM BCE)

Min NTx

(nM BCE)

Max NTx

(nM BCE)

Median NTx

(nM BCE)

Males, < 25 YOA 25 20 11 42 18
Males, 26-50 YOA 25 13 7 36.7 10.7
Males, > 50 YOA 25 11 5 24 10
Females, 18-35 YOA 25 14 8 28 13
Females, > 50 YOA 50 12 4 32 11


Limitations of the procedure:

While the ZEUS NTx Serum assay is used as an indicator of bone resorption, use of this test has not been established to predict development of osteoporosis or future fracture risk. Use of this test has not been established in primary hyperparathyroidism, hyperthyroidism, or Paget’s disease of bone. When using the ZEUS NTx Serum assay to monitor therapy, results may be confounded in patients afflicted with other clinical conditions known to affect bone resorption, e.g. metastases to bone. While the ZEUS NTx Serum assay value provides a measure of the level of bone resorption, a single ZEUS NTx Serum assay value cannot provide the rate of bone resorption as reported results do not contain a measure of time. The ZEUS NTx Serum assay results should be interpreted in conjunction with clinical findings and other diagnostic results.