Impact of IFCC healthy reference population criteria on TnT hs Gen 6 99th percentile URLs: REF-TSIX

Background Guidelines recommend high-sensitivity cardiac troponin (hs-cTn) concentrations above the 99th percentile upper reference limit (URL) to support the diagnosis of acute myocardial infarction. Because hs-cTn values are influenced by comorbidities and subclinical/silent disease, the International Federation of Clinical Chemistry (IFCC) recommends stringent criteria for defining a healthy reference population. Purpose We evaluated the impact of applying the IFCC criteria on hs-cTnT Gen 6 99th percentile URLs in the REF-TSIX Study. Methods In four global regions (United States, Europe, Japan, China) 7,910 apparently healthy adults (≥20 years) were enrolled. Lithium-heparin plasma and serum samples were prospectively collected and TnT hs Gen 6 measured on an automated high-throughput immunoassay analyser. Exclusion criteria were applied a priori (-IFCC, more liberal) and then post hoc to meet IFCC recommendations (+IFCC, more stringent) including: cardiovascular disease history/symptoms, recent chest trauma, hypertension, chronic kidney disease, diabetes, pregnancy, NT-proBNP ≥125 ng/L, treatment for hyperlipidaemia or hypertension, body mass index (BMI) <18 kg/m2 or >35 kg/m2, smoking, or other chronic diseases potentially affecting the heart (Figure 1). Uniform and sex-specific 99th percentile URLs were determined for each matrix individually and combined. Results Overall, there were 4,147 in the +IFCC and 6,533 in the -IFCC cohort of whom 52% and 49% were female, respectively; median ages were 48 and 51 years, and mean (SD) BMIs were 25.1 (3.7) and 26.3 (5.5) kg/m2 for +IFCC and -IFCC, respectively (Figure 2a). With sample matrices combined, the proportion with measurable hs-cTnT (≥ limit of detection) was high and differed by sex (81-84% of females and >99% of males in both cohorts). Applying IFCC criteria lowered the 99th percentile URLs from 24, 37, and 32 ng/L to 18, 32, and 27 ng/L for females, males and uniform cut points, respectively (Figure 2b). Across cohorts, lithium-heparin and serum URLs showed very good comparability. Conclusion Applying the stringent IFCC exclusion criteria to define a healthy reference population has a substantial impact on the hs-cTnT Gen 6 99th percentile URLs by excluding individuals with clinical or subclinical conditions associated with an elevated cTnT.