Supplementary Material for: Performance of a Novel Research-Use-Only Secretoneurin ELISA in Patients with Suspected Acute Coronary Syndrome: Comparison with an Established Secretoneurin Radioimmunoassay

<b><i>Background:</i></b> Circulating secretoneurin (SN) concentrations, as measured by established radioimmunoassay (RIA), risk stratify patients with cardiovascular disease. We now report data for a recently developed research-use-only SN enzyme-linked immunosorbent assay (ELISA) in patients with suspected acute coronary syndrome (ACS). <b><i>Methods:</i></b> SN ELISA was developed according to industry standards and tested in 401 unselected chest pain patients. Blood samples were drawn &lt;24 h from admission, and we adjudicated all hospitalizations as ACS or non-ACS. The mean follow-up was 6.2 years. <b><i>Results:</i></b> SN ELISA with 2 monoclonal sheep anti-SN antibodies has a measuring range of 10–250 pmol/L and demonstrates excellent analytical precision and accuracy across the range of SN concentrations. SN measured by ELISA and RIA correlated in the chest pain patients: rho = 0.39, <i>p</i> &lt; 0.001. SN concentrations were higher in ACS patients (<i>n</i> = 161 [40%]) than in non-ACS patients (<i>n</i> = 240) for both assays, with an area under the curve (AUC) of 0.66 (95% CI: 0.61–0.71) for ELISA and 0.59 (0.54–0.65) for RIA. SN concentrations were also higher in nonsurvivors (<i>n</i> = 65 [16%]) than survivors, with an AUC of 0.72 (0.65–0.79) for ELISA versus 0.64 (0.56–0.72) for RIA, <i>p</i> = 0.007, for difference between assays. Adjusting for age, sex, blood pressure, previous myocardial infarction, atrial fibrillation, and heart failure in multivariable analysis, SN concentrations as measured by ELISA, but not RIA, remained associated with mortality, with a hazard ratio of 1.71 (1.03–2.84), <i>p</i> = 0.038. <b><i>Conclusions:</i></b> The novel SN ELISA has excellent performance, higher AUC for diagnosis, and superior prognostic accuracy compared to the established RIA in chest pain patients.