Analytical Performance and Clinical Utility of a Sensitive Immunoassay for Determination of Human Cardiac Troponin I

Objectives: To determine the serum and plasma level of human cardiac troponin I (cTnI) resulting from myocardial damage, we have developed a sensitive and specific one-step enzyme immunoassay to measure cardiac troponin I. Design and Methods: The COBAS® cTnI assay is a semi-automated one-step solid phase immunoassay compatible with the COBAS® Core. The assay is performed in a sandwich type format using a polyclonal goat antibody capture and two highly specific horseradish peroxidase conjugated monoclonal antibody detectors directed against different epitopes of the cTnI molecule. Calibrators were made with purified recombinant cTnI. Results: The level of cTnI was determined in 84 healthy donors with no evidence of myocardial injury, resulting in a lower limit of detection (LLD) of 0.09 μg/L. The upper reference limit (URL) of the normal reference range was calculated as 0.20 μg/L. The dynamic range of the consequent EIA was between 0.09 and 6.0 μg/L with a total assay time of 45 min. Intra-assay and inter-assay variances (CVs) were ≤4%. Cross-reactivity with fast and slow skeletal troponin I was absent in concentrations up to 2.0 mg/L. Common interferents yielded negative results in the cTnI assay. Clinical utility was confirmed by measuring the circulating serum or plasma levels of cardiac troponin I in serial samples from marathon runners, clinical samples from trauma patients, and patients presenting to the Emergency Department with complaints of chest pain. Results were further evaluated using clinical diagnosis at discharge and quantified concentrations of other cardiac markers by a Stratus® analyzer and ELISA procedures. Conclusions: Results from normal and clinical samples assayed in-house for cTnI concentrations indicate that the Spectral EIA is a highly sensitive means of quantifying cTnI levels in serum and plasma for acute cardiac syndrome. The cardiac specificity of cTnI over other well-known cardiac markers is reflected in experimental results and parallel clinical diagnosis.