Evaluation of a point-of-care assay for cardiac markers for patients suspected of acute myocardial infarction.

BACKGROUND: Creatine kinase MB (CK-MB), and cardiac troponin I (cTnI) are important biomarkers for the diagnosis and rule-out of acute myocardial infarction (AMI) of patients who presented to the emergency department (ED) with chest pain. With new rapid ED assessment protocols, there is increasing pressure to produce results with a short turnaround time (TAT), and point-of-care (POC) testing is one alternative for providing fast results.

METHODS: In a multicenter study, we evaluated the analytical precision, sensitivity and specificity of the RAMP (Response Biomedical) CK-MB and cTnI POC assays and compared results against the Triage (Biosite) POC and the Dimension RxL (Dade Behring) central-laboratory assays on 365 subjects, including 185 patients suspected of AMI, and determined the normal range on 180 healthy individuals. At one site, the clinical sensitivity and specificity were estimated in 121 patients and healthy subjects with AMI using the European Society of Cardiology (ESC)/American College of Cardiology (ACC) definition of AMI. Results from healthy individuals and those with ST elevation and non-ST elevation AMI were included in a receiver operating characteristic (ROC) curve analysis.

RESULTS: Intra- and total imprecision ranged from 7.2% to 11.4% for cTnI at 0.22, 1 and 5 ng/ml and 4.8% to 8.6% for CK-MB at 7, 14 and 25 ng/ml. The upper limit of linearity was 32 ng/ml with an average recovery of 105% for cTnI and 80 ng/ml with a 106% recovery for CK-MB. The lower limit of detection was 0.03 ng/ml (10% coefficient of variance [CV] = 0.21 ng/ml) for cTnI and 0.32 ng/ml for CK-MB. The upper reference limit (normal range) was < 0.03 ng/ml for cTnI and 0-3.7 ng/ml for CK-MB. Analytical correlation against Dimension RxL were RAMP=(0.456 x RxL) + 0.11 (r = 0.988, n = 364) for cTnI and RAMP=(0.966 x RxL) + 0.60 (r = 0.986, n = 363) for CK-MB and against Triage, RAMP=(0.626 x Triage) + 0.164 (r = 0.969, n = 364) for cTnI and RAMP=(0.845 x RxL) - 0.495 (r = 0.952, n = 363) for CK-MB. On 39 AMI and 67 non-AMI patients, the clinical sensitivity, specificity and diagnostic efficiency of the cTnI and CK-MB RAMP assays were not significantly different from predicate assays.

CONCLUSIONS: The RAMP cardiac marker assays are alternatives to other FDA-cleared central laboratory and POC testing devices.