Direct comparison of clinical decision limits for cardiac troponin T and I

Objective The 99th percentile upper reference limit of high-sensitivity cardiac troponin (hs-cTn) from a healthy reference population is used for diagnosing acute myocardial infarction (AMI). Accepted current thresholds of hs-cTnT (Roche) and hs-cTnI (Abbott) are 14 and 26ng/L, respectively. Since thresholds for hs-cTnT and hs-cTnI were derived from different reference cohorts it is unclear whether they are biologically equivalent. We directly assessed sex-specific and age-specific 99th percentile upper reference limits of hs-cTnT and hs-cTnI in a single reference cohort, to investigate whether current divergent thresholds of hs-cTnT and hs-cTnI stem from intrinsic assay differences or reflect cohort variation. Methods A healthy reference population was derived from a population-based cohort (the Maastricht Study: n=3451; age: 40-75years). Individuals with diabetes mellitus, a history of cardiovascular disease, cardiac ischaemia on ECG, N-terminal pro-brain natriuretic peptide >125ng/L or estimated glomerular filtration rate <60mL/min/1.73m(2) were excluded. Non-parametric analyses were performed to assess 99th percentile upper reference limits. Results 1540 individuals were included in the healthy reference population (age 578years, 52.4% women). Overall 99th percentile upper reference limits of hs-cTnT and hs-cTnI were 15 and 13ng/L, respectively. Upper reference limits were higher in men than women (hs-cTnT: 16 vs 12ng/L), (hs-cTnI: 20 vs 11ng/L) and increased with age. Conclusions Direct comparison reveals numerically similar thresholds for hs-cTnT and hs-cTnI assays. This finding is in line with recently reported underdiagnosis of AMI with the current decision limit of 26ng/L for hs-cTnI, especially among women. Downwards adjustment of the hs-cTnI threshold, differentiated for sex, would equalise clinical decision limits for both assays, and may prevent further underdiagnosis of AMI.