Cardiac troponin I measurement with the ACCESS immunoassay system: analytical and clinical performance characteristics.

We evaluated the ACCESS cardiac troponin I (cTnI) immunoassay as a marker for myocardial infarction (MI). Total imprecision was 6.0% to 13.5%, the minimum detectable concentration was 0.007 microg/L, and the limit of quantitation was 0.046 microg/L. Comparison of cTnI measurement between the ACCESS and Stratus systems (n = 114) showed a proportional difference: ACCESS cTnI = 0.0996 Stratus cTnI + 0.049 microg/L (r = 0.811). Fifty-nine of 61 ambulatory patients without cardiac symptoms had no detectable cTnI (95% range, 0.00 to 0.025 microg/L). The optimum cutoff for discriminating MI (n = 289, 45 with MI) was 0.15 microg/L by receiver operator characteristic curve analysis; at this cutoff, the ACCESS cTnI assay showed a sensitivity of 88.9% (95% CI, 79.7-98.1%) and specificity of 91.8% (95% CI, 88.4-95.2%). The ACCESS cTnI assay results showed 89.4% and 93.0% concordance with the MB isoenzyme of creatine kinase (CK-MB) mass and Stratus cTnI results, respectively, for classification of patients with suspected MI. The ACCESS cTnI assay appears to show sensitivity and specificity comparable with those of both CK-MB mass and Stratus cTnI assays for the diagnosis of MI in patients presenting within 12 h of onset of symptoms.

In vitro interference of the red cell substitute pyridoxalated hemoglobin-polyoxyethylene with blood compatibility, coagulation, and clinical chemistry testing.

OBJECTIVES: Pyridoxalated hemoglobin-polyoxyethylene (PHP) is a prototypical red cell substitute approved for phase I studies. Peripheral blood smears of human blood mixed with PHP in 1 to 4 g/dL concentrations showed dose-dependent red cell aggregation and rouleaux. Whether this aggregation limits interpretation of blood compatibility testing and whether the intense coloration of serum or plasma containing PHP affects routine coagulation and clinical chemistry measurements was tested. DESIGN: In vitro studies. SETTING: University hospital laboratory. PARTICIPANTS: Four healthy volunteers, blood types A, B, AB, and O. All were Rh+. MEASUREMENTS AND MAIN RESULTS: ABO typing, Rh typing, and antibody screening and coagulation studies were performed on blood: PHP admixtures having final concentrations of 1, 2, and 4 g/dL. For clinical chemistry interference studies, known concentrations of analytes were added to a serum matrix containing PHP. ABO (forward) and Rh typing showed no interference in the three concentrations tested. Reverse ABO typing and antibody screening showed rouleaux at 4 g/dL, which corrected with routine saline replacement. Partial thromboplastin time (PTT), prothrombin time (PT), and fibrinogen showed no clinically significant differences from the controls. Results for electrolytes, renal function analytes, and markers of cardiac injury were acceptable by standard laboratory methods. However, results of liver function tests were unacceptable in PHP-containing specimens. CONCLUSIONS: PHP-induced aggregation was observed with high PHP concentration; however, compatibility testing was not affected because agglutination was corrected by saline replacement, which is standard practice. Although routine blood banking, coagulation, and most clinical chemistry analytes can be measured reliably, alternative methods and strategies are needed for assessing liver function in the presence of PHP.

Characteristics of a 20-minute whole blood rapid assay for cardiac troponin T.

OBJECTIVES: A qualitative whole blood rapid assay for cardiac troponin T (cTnT) was examined. The assay uses the same antibodies as for a benchmark ELISA, but the capture and detection roles were switched to enhance specificity. DESIGN AND METHODS: The cTnT Rapid Assay and ELISA were compared in 643 samples from patients having myocardial infarction, coronary artery bypass surgery, ischemic heart disease, musculoskeletal disease, renal failure, or other noncardiac conditions. Concordance between the methods was compared using the McNemar Test and cTnT cutoff of 0.2 micrograms/L. RESULTS: For the "cutoff" of 0.2 micrograms/L, concordance between the cTnT Rapid Assay and ELISA was in the range of 90-95% for each group except the renal failure patients, where concordance was 77.9%. There was no significant difference between the cTnT Rapid Assay and ELISA, except in the renal failure and ischemic heart disease patients, where there was a greater number (p < 0.05) of cTnT Rapid Assay negative results when the ELISA was > 0.2 micrograms/L. Overall concordance between the cTnT Rapid Assay and CK-MBmass was 78%. CONCLUSION: The McNemar test indicated that the cutoff for the cTnT Rapid Assay was 0.2 micrograms/L. Evidently the lower concordance among renal failure and ischemic heart disease patients reflects higher cTnT specificity for the Rapid Assay that was conferred by switching the capture and detection antibodies.

The case for cardiac troponin T: marker for effective risk stratification of patients with acute cardiac ischemia.

Availability of markers such as cardiac troponin T (cTnT) has brought new insights into ischemic heart disease (IHD). cTnT is a distinct protein that differs from other markers in biological function, molecular mass, and cytosolic pool. cTnT has been utilized for diagnosis of acute myocardial infarction (AMI) and risk stratification of patients with IHD. For AMI diagnosis, cTnT showed high sensitivity (94-100%) but generally lower specificity (46-99%), possibly because of increases in non-AMI patients with minor myocardial damage. Outcome studies have demonstrated that IHD patients with increased cTnT are at significantly greater risk for cardiac events; revascularization in patients with increased cTnT may improve outcome. Estimated costs for batched ES 300 cTnT results and for a cTnT rapid assay run "on demand" were $17.48 and $21.65, respectively. cTnT currently has no specific common procedure test code; expected reimbursement is $18.32 for the ES 300 and is not established for the rapid assay.