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Absolute and Relative Kinetic Changes of High-Sensitivity Cardiac Troponin T in Acute Coronary Syndrome and in Patients with Increased Troponin in the Absence of Acute Coronary Syndrome
Study Questions:
For patients undergoing serial assessment of high-sensitivity cardiac troponin T (hs-cTnT), is a relative or absolute change better for identifying acute coronary syndrome (ACS) and non-ACS patients?
Methods:
The authors serially measured hs-cTnT in 784 consecutive patients without ST elevation or left bundle branch block presenting to the emergency department who underwent an evaluation for ACS. Patients with ACS who had at least two hs-cTnT measurements within 6 hours and non-ACS patients with hs-cTnT concentrations above the 99th percentile value (14 ng/L) were studied to compare absolute and relative kinetic changes of hs-cTnT.
Results:
For discrimination of non–ST-elevation myocardial infarction (NSTEMI) (n = 165), the absolute change using the receiver operating characteristic (ROC)-optimized value of 9.2 ng/L had a positive and negative predictive value of 49% and 96.5%, an area under the curve of 0.898, and was superior to all relative hs-cTnT changes (p < 0.0001). In contrast, relative changes had an area under the curve of only 0.752. In the NSTE-ACS group (n = 342), the absolute change using an ROC-optimized value of 6.9 ng/L had a positive and negative predictive value of 83% and 93%. When compared to the ≥20% relative change, the ROC-optimized absolute change added significantly to both the entire study population and the ACS cohort (net reclassification index 0.331 and 0.499, p < 0.0001).
Conclusions:
The authors concluded that absolute changes appear superior to relative changes in hs-cTnT for discriminating between patients with and without NSTEMI. A rise or fall of at least 9.2 ng/L in the overall study population performed well for excluding NSTEMI. However, δ-values are useful to rule-in NSTEMI only in a specific ACS population.
Perspective:
This is another analysis suggesting that with high-sensitivity assays, an absolute change is better than a relative change in distinguishing those with from those without AMI. This was particularly the case in patients who presented later after the onset of symptoms, and might be explained by higher levels in the initial samples. There is an important difficulty in this entire area that should be considered, which is the criteria for the gold standard diagnosis. In this study, an arbitrary though reasonable change of 20% and an absolute difference of 5 ng/L was used over a 24-hour period. Most, if not all patients at this center underwent coronary angiography. It should be appreciated that the mere presence of coronary artery disease does not necessarily mean unstable coronary artery disease and there are other etiologies for cTnT elevations, and it is unclear how individual cases were handled. Finally, it should be appreciated that especially at higher values, the amount of change will be less than spontaneous conjoint biological and analytical variation, meaning that some patients could meet the cTnT criteria due to variability alone.
Keywords: Coronary Artery Disease, Myocardial Infarction, Acute Coronary Syndrome, Biomarkers, Coronary Angiography, Cardiovascular Diseases, Bundle-Branch Block, ROC Curve, Troponin
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