Kamstrup, Pia R.

Abstract Background/Introduction Macrotroponin refers to high-molecular-weight troponin complexes bound to immunoglobulins, shown to cause persistently elevated troponin values often unrelated to myocardial injury. We hypothesized that its frequency might increase with age and differ between men and women, reflecting potential age-related cardiac changes and sex-specific risk profiles. Purpose To assess whether macrotroponin frequency varies across age groups and by sex within the upper sex-specific 90th percentile of troponin values in a healthy Danish reference population. Methods Among 1,307 participant samples with normal-range NT-proBNP, HbA1c, and eGFR ≥90 mL/min/1.73m2, 147 samples with troponin I within the upper levels of the sex-specific 90th percentile for the Siemens Atellica assay were further tested for macrotroponin I using Protein A/G immunoglobulin depletion and sucrose gradient ultracentrifugation. Samples were only deemed macrotroponin-positive by concordantly positive results. After excluding 29 samples with low troponin values due to analytical dilution constraints, 118 participants remained. Macrotroponin I frequency was compared across three age groups (<40, 40–60, and >60 years) and between sexes. Logistic regression was used to adjust for creatinine levels. Results Of 118 samples tested (48% females), macrotroponin I was present in 88 (75%), with similar frequencies in women (80%) and men (77%). Macrotroponin I frequency did not differ significantly across age groups (p=0.26) or between sexes (p>0.5) (Table 1, Figure 1). Logistic regression revealed no significant associations between macrotroponin I and age group, sex, or creatinine levels (all p > 0.5). Conclusion Macrotroponin I was highly frequent in the highest troponin ranges in a healthy reference population and showed no relationship with age or sex. The presence of macrotroponin I may impact clinical management in a considerable number of patients, but further investigation is required in clinical studies.

Abstract Background Cardiac troponin (cTn) levels exceeding the 99th percentile upper reference limit and a rise/fall pattern are key for diagnosing myocardial injury and infarction. Macrotroponins, formed by patient anti-cTn antibodies targeting cTn, can cause persistently elevated cTn levels without ongoing myocardial injury. The frequency and impact of macrotroponin interference on cTn 99th percentiles are unclear. This study compares sex-specific 99th percentiles for 2 cTn assays, before and after excluding macrotroponin-positive samples, focusing on the top 10% of cTn levels. Methods We examined 1058 plasma samples from healthy individuals previously used for Danish cTn 99th percentiles. Following International Federation of Clinical Chemistry and Laboratory Medicine educational recommendations, macrotroponin presence was assessed in the top 10% cTn samples using immunoglobulin G (IgG) depletion screening and a reference sucrose gradient, confirming macrotroponin when both methods concurred. Due to analytical dilution constraints, [the highest] 88 of 135 Siemens Atellica high-sensitivity cTnI (hs-cTnI) samples were analyzed with both methods. All 106 Roche hs-cTnT samples were negative using IgG depletion, and sucrose analysis was limited to the highest 70 samples. Results Macrotroponin was found in 76% (67/88) of Siemens samples but in none of the Roche samples (0/70). Excluding macrotroponin-affected samples lowered the Siemens 99th percentiles from 117 ng/L to 22 ng/L in men and from 37 ng/L to 9 ng/L in women. The 99th/50th percentile ratio for Siemens decreased from 12- to 29-fold to 3- to 7-fold, approaching the Roche ratios. Conclusions Macrotroponin significantly influenced the Siemens Atellica hs-cTnI 99th percentiles, suggesting important clinical implications that warrant further prospective studies. The 99th/50th percentile ratio may help evaluate macrotroponin interference in troponin assays.

BACKGROUND: Cardiac troponin (cTn) is key in diagnosing myocardial infarction (MI). After MI, the clinically observed half-life of cTn has been reported to be 7 to 20 hours, but this estimate reflects the combined elimination and simultaneous release of cTn from cardiomyocytes. More precise timing of myocardial injuries necessitates separation of these 2 components. We used a novel method for determination of isolated cTn elimination kinetics in humans. METHODS: Patients with MI were included within 24 hours after revascularization and underwent plasmapheresis to obtain plasma with a high cTn concentration. After at least 3 weeks, patients returned for an autologous plasma retransfusion followed by blood sampling for 8 hours. cTn was measured with 5 different high-sensitivity cTn assays. RESULTS: Of 25 included patients, 20 participants (mean age, 64.5 years; SD, 8.2 years; 4 women [20%]) received a retransfusion after a median of 5.8 weeks (interquartile range, 5.0–6.9 weeks) after MI. After retransfusion of a median of 620 mL (range, 180–679 mL) autologous plasma, the concentration of cTn in participants’ blood increased 4 to 445 times above the upper reference level of the 5 high-sensitivity cTn assays. The median elimination half-life ranged from 134.1 minutes (95% CI, 117.8–168.0) for the Elecsys high-sensitivity cTnT assay to 239.7 minutes (95% CI, 153.7–295.1) for the Vitros high-sensitivity cTnI assay. The median clearance of cTnI ranged from 40.3 mL/min (95% CI, 32.0–44.9) to 52.7 mL/min (95% CI, 42.2–57.8). The clearance of cTnT was 77.0 mL/min (95% CI, 45.2–95.0). CONCLUSIONS: This novel method showed that the elimination half-life of cTnI and cTnT was 5 to 16 hours shorter than previously reported. This indicates a considerably longer duration of cardiomyocyte cTn release after MI than previously thought. Improved knowledge of timing of myocardial injury may call for changes in the management of MI and other disorders with myocardial injury.