Utility of Absolute and Relative Changes in Cardiac Troponin Concentrations in the Early Diagnosis of Acute Myocardial Infarction

Study Questions:

Are early absolute rises in cardiac troponin (cTn) concentrations using a high-sensitivity (hs) assay better than relative rises in cTn for diagnosis of acute myocardial infarction (AMI)?

Methods:

The diagnostic accuracy of absolute and relative (%) changes in cTn were determined in 836 patients presenting to the emergency room with symptoms suggestive of AMI. Blood samples for the determination of hs cTnT and cTnI ultra were collected at presentation and after 1 and 2 hours in a blinded fashion. The final diagnosis was adjudicated by two independent cardiologists.

Results:

The area under the receiver operating characteristic (ROC) curve for diagnosing AMI was significantly higher for 2-hour absolute versus 2-hour relative (%) cTn changes ([95% CI], hs cTnT, 0.95 [0.92-0.98] vs. 0.76 [0.70-0.83], p < 0.001; cTnI ultra, 0.95 [0.91-0.99] vs. 0.72 [0.66-0.79], p < 0.001). The ROC–derived cutoff value for 2-hour absolute change was 0.007 µg/L for hs cTnT and 0.020 µg/L for cTnI ultra. Absolute changes were superior to relative changes in patients with both low and elevated baseline cTn levels.

Conclusions:

Absolute changes of cTn levels have a significantly higher diagnostic accuracy for AMI than relative changes, and seem, therefore, to be the preferred criteria to distinguish AMI from other causes of cTn elevations.

Perspective:

High-sensitivity assays for cTns have been developed that are useful for the early diagnosis of MI in patients presenting with ischemic symptoms. However, elevations of hs cTns greater than the ‘99th percentile’ are common, apparently due to factors other than AMI. Therefore, the rise and fall of the cTn level becomes very important in establishing the proper diagnosis. Criteria for a ‘positive’ rise are not established. This study demonstrates that absolute changes, regardless of baseline Tn level, are more useful than relative changes of cTn in confirming the diagnosis of MI. The cutoff value for significant rise is approximately one half the 99% values for the assays used in this study.

Keywords: Myocardial Infarction, Cytoskeletal Proteins, Diterpenes, Biological Markers, Early Diagnosis, Troponin I, Cardiology, Troponin T, Receptors, Transforming Growth Factor beta, Emergency Service, Hospital


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