False-positive cardiac troponin I in a routine clinical population

Abstract

Two-site immunoassays are often used to measure serum cardiac troponin I (cTnI); these contain 2 antibodies specific at 2 different sites for the intended analyte. The first antibody, the “capture” antibody, binds to any cTnI in the serum sample. The second antibody, the “label” antibody, is added after a wash phase and binds any “captured” cTnI. The label antibody provides a luminescent signal. The intensity of this signal is measured by the instrument after a final wash phase and used to quantify cTnI levels. Serum constituents may interfere with this process and lead to inaccurate quantification. Human antibody specific for the Fc portion of the assay species immunoglobulin (heterophilic antibodies) may crosslink the label and capture antibodies in the absence of the intended analyte. 1 Kricka L.J. Schmerfeld-Pruss D. Senior M. Goodman D.B. Kaladas P. Interference by human anti-mouse antibody in two-site immunoassays. Clin Chem. 1990; 36: 892-894 PubMed Google Scholar Most modern immunoassays contain a nonspecific antibody of the assay species intended to mop up any heterophilic antibody present in serum. 2 Boscato L.M. Stuart M.C. Incidence and specificity of interference in two-site immunoassays. Clin Chem. 1986; 32: 1491-1495 PubMed Google Scholar However, in the presence of sufficient quantities of interfering antibodies analytic errors may still occur. Furthermore, nonantibody-mediated interference with analyte measurement has also been described. Residual fibrin and other microparticles may interfere with analyte measurement. 3 Beyne P. Vigier J.P. Borgoin P. Vidaud M. Comparison of single and repeat centrifugation of blood specimens collected in BD evacuated blood collection tubes containing a clot activator for cardiac Troponin I assay on the ACCESS Analyzer. Clin Chem. 2000; 46: 1869-1870 PubMed Google Scholar , 4 Nosanchuk J.S. False increases of troponin I attributable to incomplete separation of serum. Clin Chem. 1999; 5: 714 Google Scholar The prevalence of clinically significant inaccurate quantification of cTnI is unknown. This study describes the prevalence of false-positive cTnI in a routine clinical setting.