N-Telopeptide Cross-links (NTx), Urine

CPT: 82523; 82570
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Test Details

Synonyms

  • Collagen Cross-linked N-Telopeptide
  • N-Telopeptide
  • NTx Test
  • Osteomark®

Use

Evaluation of osteoporosis and assessment of antiresorptive therapy

Methodology

Ortho Vitros Enhanced Chemiluminescence System

Reference Interval

• Pediatric: see table.1

• Adults:

− Male: 0−62 nM BCE/mmol creatinine

− Female: 20 to 49 years 0−64 nM BCE/mmol creatinine; >49 years 0−89 nM BCE/mmol creatinine

Tanner Stage

Male

(nM BCE/mmol creatinine)

Female

(nM BCE/mmol creatinine)

I

55−508

6−662

II

21−423

193−514

III

27−462

13−632

IV

<609

<389

V

<240

<132

Additional Information

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.1 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. Osteoporosis occurs when there is an imbalance between bone formation and bone resorption leading to net bone loss.2-5 Certain aspects of this bone composition and structure that contribute to increased bone fragility may not be captured by bone mineral density measurements.5

Bone resorption by osteoclasts results in the production of cross-linked N-telopeptides of type I collagen (NTx).1 NTx is specific to bone and is found in urine as a stable end product of bone degradation. Levels of NTx correlate with the rate of bone resorption. Bone resorption rates exceeding bone formation results in a net loss of bone and ultimately osteopenia or osteoporosis.2-8 Osteoporotic fractures are a major source of morbidity and mortality in older women.2 The NTx test is intended for use in predicting skeletal response to hormonal antiresorptive therapy in postmenopausal women. The NTx test can also be used to monitor the efficacy of antiresorptive therapy7 in postmenopausal women, women with osteoporosis, and individuals with Paget disease. The NTx test can also be used in monitoring the effect of estrogen-suppressing therapies on the rate of bone resorption. A recent study8 supported the use of NTx to identify the probability of a decrease in bone mineral density after one year in postmenopausal women receiving a calcium supplement relative to those treated with hormonal antiresorptive therapy.

Several studies have shown that certain biochemical markers of bone turnover, measured in serum or urine, can be used as independent predictors of fractures, especially spine and hip.2,6 Bone mineral density (BMD) is often used to monitor the efficacy of osteoporosis treatment and to follow patient compliance. Unfortunately, changes in BMD in response to treatment are slow, and it takes at least one year of treatment before a significant change in BMD can be observed in many cases.2,7 As a result, the absence of BMD increase does not necessarily indicate a lack of therapeutic response.2,7 The use NTx can be helpful for assessing early changes in BMD (baseline vs post-treatment) revealing a biological effect of the medication and proving patient compliance and persistence.2,7

Specimen Requirements

Specimen

Urine

Volume

20 mL

Minimum Volume

1 mL

Container

Plastic urine container without preservative

Collection

Collect a second void of the morning or an aliquot of a 24-hour urine (no preservative). When monitoring therapy, baseline samples should be collected prior to initiation of therapy. Subsequent specimens should be collected at the same time of day as baseline specimens.

Storage Instructions

Refrigerate.

Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Quantity not sufficient for analysis; whole blood contamination; hemolysis; specimen containing preservative

Clinical Information

Special Instructions

Values obtained with different assay methods should not be used interchangeably in serial testing. It is recommended that only one assay method be used consistently to monitor each patient's course of therapy. This procedure does not provide serial monitoring; it is intended for one-time use only. If serial monitoring is required, please order test 511097.

Footnotes

1. Endres DB, Rude RK. Mineral and bone metabolism. In Burtis CA, Ashwood ER, eds. Tietz Textbook of Clinical Chemistry. 3rd ed. Philadelphia, Pa: WB Saunders Co; 1999:1349-1457.9799819
2. Sweet MG, Sweet JM, Jeremiah MP, Galazka SS. Diagnosis and treatment of osteoporosis. Am Fam Physician. 2009 Feb 1; 79(3):193-200.19202966
3. Bergmann P, Body JJ, Boonen S, et al. Evidence-based guidelines for the use of biochemical markers of bone turnover in the selection and monitoring of bisphosphonate treatment in osteroporosis: A consensus document of the Belgian Bone Club. Int J Clin Pract. 2009 Jan; 63(1):19-26.19125989
4. Lewiecki EM. Managing osteoporosis: Challenges and strategies. Cleve Clin J Med. 2009 Aug; 76(8):457-466.19652039
5. Poole KE, Compston JE. Osteoporosis and its management. BMJ. 2006 Dec 16; 333(7581):1251-1256.17170416
6. Singer FR, Eyre DR. Using biochemical markers of bone turnover in clinical practice. Cleve Clin J Med. 2008 Oct; 75(10):739-750.18939390
7. Garnero P, Shih WJ, Gineyts E, Karpf DB, Delmas PD. Comparison of new biochemical markers of bone turnover in late postmenopausal osteoporotic women in response to alendronate treatment. J Clin Endocrinol Metab. 1994; 79(6):1693-1700.7989477
8. Garnero P, Sornay-Rendu E, Chapuy MC, Delmas PD. Increased bone turnover in late postmenopausal women is a major determinant of osteoporosis. J Bone Miner Res. 1996 Mar; 11(3):337-349.8852944

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
141093 N-Telopeptide, Urine 511095 N-telopeptide nmol BCE 27939-8
141093 N-Telopeptide, Urine 013672 Creatinine, Urine mg/dL 2161-8
141093 N-Telopeptide, Urine 511117 N-telo/Creat. Ratio nM BCE/mM Cr 14115-0
141093 N-Telopeptide, Urine 511495 Interpretive Guide: N/A

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