The concentration of long cardiac troponin T forms is independent of age and common comorbidities in patients referred for elective open-heart surgery

Background High-sensitivity cardiac troponin T (hs-cTnT) is a cornerstone of the diagnosis of myocardial infarction (MI), but mild elevations of hs-cTnT are common also in chronic cardiac conditions. Early troponin release in type 1 MI is dominated by large cTnT-I-C complexes, yet the current commercial hs-cTnT assay detects both intact and fragmented cTnT forms. To potentially enable more specific detection of myocardial injury, a novel immunoassay has been developed to selectively measure only intact and mildly truncated cTnT (“long cTnT”). The influence of age and comorbidities on these long cTnT forms is unknown in patients with severe heart disease but no MI. Purpose To determine whether long cTnT is less affected by age and comorbidities than hs-cTnT in patients referred for elective open-heart surgery. Methods Lithium-heparin plasma samples were collected from 144 patients before elective open-heart surgery. Participants were clinically stable at the time of sampling. Long cTnT was measured using a novel immunoassay and hs-cTnT with the Elecsys Troponin T hs kit (cobas e801, Roche Diagnostics). The influence of age and comorbidities (dyslipidemia, diabetes, hypertension, heart failure, atrial fibrillation, coronary artery disease and pulmonary hypertension) on long cTnT and hs-cTnT concentrations was evaluated. Results The median [25th-75th percentile] age of the study population was 66 [58-71] years. The median hs-cTnT and long cTnT concentrations were 12.0 [8.0-19.0] and 3.9 [2.6-5.8] ng/l, respectively. The hs-cTnT and long cTnT concentrations exceeded their 99th percentile upper reference limit (URL) in 42% and 15% of patients, respectively. Long cTnT concentrations remained low regardless of age and showed no significant correlation with age (Spearman’s rs = 0.106, p = 0.207), whereas hs-cTnT concentrations demonstrated a moderate positive correlation with age (rs = 0.354, p < 0.001) (Figure 1). The hs-cTnT concentrations were significantly associated with all of the studied comorbidities, with median concentrations near or above the 99th percentile URL (Table 1). The long cTnT concentration was significantly associated only with diabetes (p = 0.031) and hypertension (p = 0.010), and median concentrations remained below the 99th percentile URL in all comorbidity groups (Table 1). Conclusions Unlike the hs-cTnT concentration, the long cTnT concentration is only minimally influenced by age and comorbidities. This suggests that long cTnT forms may enable more specific detection of myocardial injury regardless of age and common chronic comorbidities.