crosslinked N-telopeptide in urine; urine pyridinolone & deoxypyridinolone (OsteoMark)

Introduction

Urinary marker of bone resorption.

Reference interval

• male: 23-110 NTx*
• female: 13-96 NTx

* NTx = umol bone collagen equivalents (BCE)/mol of creatinine

Clinical significance

• cross-linked N-telopeptides are formed by collagenase digestion of bone-mineral matrix
• cross-linked N-telopeptides are excreted in the urine & appear to be specific markers of bone resorption
• the assay is especially useful for management of bone loss in osteoporosis*

* Probability of a decrease in bone mineral density with NTx

NTx	Probability of decrease
18-38	1.4 p=0.28
38-51	2.4 p=0.03
51-67	3.8 p=0.0006
67-188	17.3 p=0.0001

Increases

• clinical disorders
  • Paget's disease
  • hyperparathyroidism
  • osteoporosis

Methods

• ELISA
• assays measure N-telopeptide fragments of collagen (non-helical amino-terminal fragments)
• these fragments contain both pyridinolone & deoxypyridinolone
• assays are calibrated using a standard of bacterial collagenase-digested human bone collagen
• results are expressed as equivalent moles of bone collagen type 1 normalized to creatinine

Specimen

• urine (2 hour)
• collect after 8 hour fast
• store frozen

More general terms

• collagen crosslinks
• urine chemistry test

Component of

• crosslinked N-telopeptide/creatinine in urine