Single-sample rule out pathway for acute myocardial infarction using the Alinity high-sensitivity cardiac troponin I assay

Background High-sensitivity cardiac troponin (hs-cTn) assays have enabled safe early discharge of patients at very low risk for myocardial infarction. We previously developed a single-sample rule out pathway using the ARCHITECT hs-cTnI assay and showed that it was safe and effective when implemented in practice. In a secondary analysis of the POC-ET (Point of Care Evaluation of High-sensitivity Cardiac Troponin) study, we evaluated this pathway with the Alinity hs-cTnI assay. Methods Patients presenting with possible myocardial infarction in the POC-ET (NCT05665127) study were included. The primary outcome was type 1, 4b or 4c myocardial infarction or cardiac death at 30 days. Cardiac troponin I (cTnI) was measured in stored materials at presentation and at 2 hours using the ARCHITECT and Alinity hs-cTnI assays. The sex-specific 99th percentile upper reference limit (URL) are 34 ng/L in male and 16 ng/L in female for both assays. Agreement was assessed with Bland-and-Altman method, Passing Bablok regression, and Pearson’s correlation coefficient. Distributions of presentation values were compared with KS test. Pathway performance was evaluated in the overall population and prespecified subgroups, excluding those with ischaemia on the electrocardiogram. The negative predictive value (NPV) and sensitivity were determined and proportion of patients identified as low and high risk compared with McNemar's test. Results In 986 patients (60 [51-70] years, 38% female), 78 (7.9%) had a primary outcome. Strong agreement was found in the raw cTnI measurements (99% samples within the limit of agreement; correlation coefficient : 0.98 [0.96-0.97], P<0.001; Passing Bablok regression: slope 1.12 [1.11-1.13], intercept -0.16 [-0.18 to -0.13]). At presentation, distributions of cTnI values determined by the two assays were similar (Figure 1, P=0.810). Both assays showed comparable diagnostic performance using a risk stratification threshold of <5 ng/L and the sex-specific diagnostic threshold, with identical NPV (100 [99.6-100]%) and sensitivity (100 [95.6-100]%) and similar proportions of patients stratified as low- (Alinity 67% versus ARCHITECT 67%) and high-risk (10% versus 9%). Overall, both assays identified 86% and 14% of patients as low- or high-risk, respectively (P=1.0; Figure 2). The corresponding NPV and sensitivity were 100 (99.7-100)% and 100 (95.6-100)% with Alinity, and 99.7 (99.0-99.9)% and 95.2 (85.6-99.0)% for ARCHITECT. Similar performance was observed across subgroups stratified by age, sex, symptom duration, history of myocardial infarction, and renal function. Conclusions The Alinity and ARCHITECT hs-cTnI assays can be used interchangeably in clinical practice with comparable safety, efficacy, and performance within a single-sample rule out pathway for patients with suspected acute coronary syndrome.