Development of monoclonal antibodies for an assay of cardiac troponin-i and preliminary results in suspected cases of myocardial infarction

Abstract

To improve the specificity of biochemical markers of myocardial infarction (MI), we have developed a double monoclonal "sandwich" enzyme immunoassay to measure cardiac troponin-I (cTnl) in serum. We produced eight IgG monoclonal antibodies against human cardiac troponin-I (cTnl) and tested them against human and animal (canine, bovine, and rabbit) troponins. Five antibodies were cardiac-specific; none of the antibodies were species-specific. Two of the five cTnl-specific monoclonal antibodies were utilized in an immunoassay. Standards were made by adding purified human cTnl to affinity-stripped cTnl-free human sera to cover the range 0-100 μg/L for cTnl. The dose-response curve was nonlinear but reproducible. Total assay imprecision (CV) varied between 11% and 21%. The upper limit of the reference range (nonparametric 95% interval) was established as 3.1 μg/L by measuring cTnl concentration in sera of 159 hospitalized patients without evidence of cardiac disease. Purified human skeletal Tnl up to 10 000 μg/L did not affect the assay (calculated cross-reactivity <0.1%). Diagnostic sensitivities of creatine kinase MB isoenzyme (CK-MB) and cTnl were evaluated retrospectively in 49 consecutive patients with proven MI. In the 30 patients for whom sufficient information was available to establish an accurate time course, CK-MB was more sensitive during the first 4 h after the onset of chest pain, but thereafter the sensitivities were similar up to 48 h. However, cTnl is more cardiac-specific than is CK-MB and remains increased longer than does CK-MB.