Kai M. Eggers

BACKGROUND: Cardiac troponin is increasingly used for cardiovascular risk prediction. While abnormal values often reflect subclinical cardiovascular disease, they can be raised due to interference, where antibodies influence the assay or clearance of troponin from the circulation by forming macrotroponin complexes. The frequency of macrotroponins and its association with future risk are unknown. METHODS: In a general population cohort, participants with both cardiac troponin I and T measurements available (n=19 499, median 49 [25th–75th percentile, 36–58] years of age, 58.3% women) were categorized into 3 groups: no myocardial injury (neither cardiac troponin I or T was elevated), suspected macrotroponin (either cardiac troponin was elevated and discordant with a >3-fold difference in concentration), and myocardial injury (either cardiac troponin was elevated without discordance). Macrotroponin complex formation was verified in a subset of samples (n=203) using immunoglobulin depletion and ultracentrifugation. Associations with future myocardial infarction, ischemic stroke, or cardiovascular death were evaluated using Cox proportional hazards models adjusted for known cardiovascular risk factors. The generalizability of our findings was determined through replication in a second general population cohort study. RESULTS: Elevated cardiac troponin I was present in 1% (193 of 19 499) of participants and elevated cardiac troponin T in 6% (1159 of 19 499). Among those, 48% and 57% were discordant, respectively. Biochemical testing attributed 92.5% of discordant troponin I and 15.4% of discordant troponin T to macrotroponin complexes. Participants with myocardial injury were at increased risk of future cardiovascular events compared with those without (cardiac troponin I: adjusted hazard ratio [HR], 2.90 [95% CI, 1.99–4.22]; cardiac troponin T: adjusted HR, 1.99 [95% CI, 1.63–2.42]), whereas those with suspected macrotroponin had similar risk as those without elevated values for suspected macrotroponin I (adjusted HR, 1.59 [95% CI, 0.94–2.70]) and T (adjusted HR, 1.27 [95% CI, 1.00–1.61]). Findings were similar in the replication cohort. CONCLUSIONS: Assay interference due to macrotroponin complex formation is common in individuals with elevated cardiac troponin concentrations in the general population, particularly for cardiac troponin I. This has important implications for the use of cardiac troponin testing for cardiovascular risk assessment in the general population.

Background: High-sensitivity cardiac troponin (hs-cTn) assays are recommended for the diagnosis of acute myocardial infarction. Here, we characterize the analytical performance of a next-generation hs-cTn assay, Elecsys® Troponin T hs Gen 6 (Roche Diagnostics International). Methods: Surplus lithium-heparin plasma or serum samples from patients or healthy volunteers were run on Cobas® e 801, e 402, and Pro analyzers. Limits of blank (LoB), limits of detection (LoD), and limits of quantitation (LoQ) were determined according to CLSI EP17-A2, with target values of 1.0 and 1.5 ng/L for LoB/LoD and 3.0 ng/L (10% CV) and 1.5 ng/L (20% CV) for LoQ, respectively. Precision was measured, per CLSI EP17-A2, using 3 QC samples (approximately 4, 30, and 220 ng/L), 12 native samples, and 3 reagent lots. Linearity, per CLSI EP06-Ed2, was determined by diluting samples with cardiac troponin T (cTnT) concentration above the measuring range with a low/blank sample. Interference (per Glick) with endogenous and assay components at 5 cTnT concentrations was assessed. Results: Measured values for LoB, LoD, and LoQ at 10% and 20% CV were 0.1 to 0.7 ng/L, 0.3 to 1.4 ng/L, 1.0 to 2.9 ng/L, and 0.4 to 1.2 ng/L, respectively. Repeatability CVs were 1.0 to 5.8% for mean cTnT concentrations of 2.6 to 9230 ng/L in lithium-heparin plasma. High precision was shown across lots, and linearity was observed across the measuring range (1.5 to 9500 ng/L, all Pearson's r = 1.00). No interferences were observed, specified up to ≤1000 mg/dL hemoglobin, ≤50 mg/dL [≤855 µmol/L] icterus/bilirubin, and ≤1200 ng/mL biotin. Conclusions: The analytical performance characterization of the assay demonstrated high sensitivity, high precision at the low end and across the measuring range, and resistance to interference.

Background: Measurement of cardiac troponin (cTn) using high-sensitivity assays is recommended for the diagnosis of myocardial infarction. We determined sex-specific and uniform 99th percentile upper reference limits (URLs) using the new Elecsys® Troponin T high-sensitivity Gen 6 assay in a global, healthy reference range cohort. Methods: Lithium-heparin plasma and serum samples were prospectively collected from apparently healthy individuals aged ≥20 years across 34 global sites in the United States, Europe, China, and Japan. cTnT was measured using the Troponin T high-sensitivity Gen 6 assay on the Cobas® e 801 analyzer. Exclusion criteria were defined according to the 2022 IFCC guidance. Uniform and sex-specific 99th percentile URLs and nonparametric 95% CIs were determined in plasma and serum separately and combined. Results: The final study population comprised 4147 participants (52.5% female) with a median (25th–75th percentiles) age of 48.0 (33.0–59.0) years; 45.8%, 47.9%, 5.2%, and 1.1% were White, Asian, Black, and other/unknown, respectively. For sample matrices combined (n = 8294), 81.0% and 99.2% of cTnT values were above the limit of detection in females and males, respectively. Sex-specific 99th percentile URLs (95% CI) were 18 (16–23) ng/L for females and 32 (28–35) ng/L for males; the uniform 99th percentile URL was 27 (24–31) ng/L. URLs were comparable in plasma and serum samples. Conclusions: This study determined sex-specific and uniform 99th percentile URLs for the Troponin T high-sensitivity Gen 6 assay that were comparable irrespective of the matrix used in a large, global, healthy reference population.

Background: Emerging evidence suggests that the ratio between cardiac troponin (cTn) I and T may provide information on the risk of adverse outcomes in individuals with cardiovascular disease. Whether the cTn I/T ratio provides prognostic insights in the general population is unknown. Methods: The cTn I/T ratio was calculated in 8855 participants (43% female, median age 56 years) from the Generation Scotland Study where both cTnI and cTnT concentrations were above the limit of blank. Multivariable cause-specific Cox proportional hazard models were used to estimate the associations between cTn I/T ratio and the primary outcome of cardiovascular or non-cardiovascular death. Results: The median cTn I/T ratio was 0.5 (25th–75th percentile, 0.3–0.8) and median follow-up was 11.4 (10.8–12.7) years. Individuals in the highest ratio tertile (≥0.64) were more likely to be male, have a higher body mass index and systolic blood pressure, and a history of cardiovascular disease. Those in the lowest ratio tertile (<0.38) were more likely to be smokers or have diabetes. After adjustment for cardiovascular risk factors, the cTn I/T ratio was positively associated with cardiovascular death (per doubling increase, adjusted hazard ratio [HR] 1.16 [95% CI, 1.05–1.28]), while an inverse association was observed for non-cardiovascular death (HR 0.89 [95% CI, 0.81–0.99]). Conclusions: The cTn I/T ratio is positively associated with cardiovascular death in the general population, while inversely associated with non-cardiovascular death. Future research is needed to unravel underlying mechanisms and determine whether the cTn I/T ratio provides valuable information regarding risk of cardiovascular and non-cardiovascular mortality to guide further management.

The 99th percentile of cardiac troponin assays for determining the presence of acute myocardial infarction (AMI) was set when assay analytical performance was much less precise than currently and was chosen, in part, to reduce the frequency of ‘false-positive’ results. A result greater than 99th percentile criterion has been a requirement of each version of the universal definition of MI. It also became used as a dichotomous decision-making threshold in diagnostic strategies for investigating AMI in acute care settings. There are numerous difficulties in deriving the 99th percentile which undermine its reliability as a standalone test threshold. It is important for patient safety that all users are aware of the challenges and pitfalls of using the 99th percentile for decision-making. We present a focused review of the 99th percentile, highlighting some difficulties with its use as a decision threshold as well as possible adjunctive strategies and alternative approaches.