The Vitros N-terminal telopeptide (NTx) assay is a competitive immunoassay technique that depends on competition between NTx in the sample with a synthetic NTx peptide coated on the wells for binding by a horseradish peroxidase (HRP)-labeled antibody conjugate (mouse monoclonal anti-NTx). The conjugate is captured by the peptide coated on the wells and unbound materials are removed by washing.
A reagent containing luminogenic substrates (a luminol derivative and a peracid salt) and an electron transfer agent (a substituted acetanilide) are added to the wells. The HRP in the bound conjugate catalyzes the oxidation of the luminol derivative, producing light. The electron transfer agent increases the level of light produced and prolongs the duration of light produced. The light signals are read by the Vitros System. The amount of HRP conjugate bound is inversely proportional to the concentration of NTx in the sample. Assay values are corrected for urinary dilution by urinary creatinine analysis and expressed in nanomoles bone collagen equivalents per liter (nM BCE/L) per millimole creatinine per liter (mM creatinine/L).(Instruction manual: Vitros Instructions for Use, N-Telopeptide. Ortho-Clinical Diagnostics, Inc. version 1.0; 100 Indigo Creek Drive, Rochester, NY 14626-1501 version 2.1 9/16/2009)