Cardiac troponin (cTn) assays have been widely used worldwide to assess myocardial injury. Recently, new high sensitivity cardiac troponin (hs-cTn) methods have been introduced. A JACC scientific expert panel provided instructions and recommendations for institutions experiencing the transition from traditional to hs-cTn assays.
The innovative hs-cTn assays allow more precise troponin detection at lower concentrations, as compared to traditional methods, due to a better signal-to-noise ratio provided by the presence of specific antibody reagents. Importantly, the unit of measure for reporting hs-cTn concentrations is ng/l instead of the previously used ng/ml for cTn. The ng/l unit of measure results in integer numbers for troponin concentration instead of fractional ones (e.g. 25 ng/l vs 0.025 ng/ml), potentially increasing clarity and safer clinical interpretation. Concerning cutoff values for hs-cTn, Januzzi et. al advise to adopt gender-specific ones for decision-making.
A crucial aspect concerning troponin testing is establishing standardized protocols to diagnose acute myocardial infarction (AMI) in emergency department (ED) patients with acute coronary syndrome (ACS) symptoms. An increase in troponin above the 99th percentile of a normal population is generally considered abnormal. However, increased troponin alone, which identifies myocardial injury, is not enough to diagnose AMI. Serial sampling and changes in hs-cTn, together with coronary ischemic symptoms, are essential for AMI diagnosis. The expert panel advises to establish specific cutoffs for each individual to identify rise and fall in hs-cTn, based on respective baseline concentration values. Suggested changes in thresholds range from 50 to 80% of baseline troponin concentration. Currently, so-called accelerated diagnostic protocols (ADP) are used in ED to rule out the presence of AMI. Therefore, these rapid algorithms need to have high sensitivity and high negative predictive value, minimizing the risk of post-discharge complications. For early presenters (less than 3 hours from symptom onset), the advised procedure is to perform serial testing of hs-cTn (baseline measurement plus a second one after 1, 2 or 3 hours), to be assessed together with a validated risk score, such as HEART (History, ECG, Age, Risk Factors and Troponin) or EDACS (Emergency Department Assessment of Chest Pain Score). For patients presenting after 3 hours from symptom onset, it is suggested to examine hs-cTn at baseline and after 1 hour. In patients > 3 hour symptom onset, a single hs-cTn test is advised for ruling out MI, whereby very low troponin concentration (less than the limit of detection) and no ischemia on the ECG would be sufficient.
For non-ED patients in the hospital setting with acute chest pain symptoms, a baseline plus 3 hour hs-cTn measurement approach is advised. Caution in the results’ interpretation should be taken by assessing the whole clinical scenario and by considering that the presence of comorbidities, such as diabetes mellitus, chronic kidney disease, heart failure and left ventricular hypertrophy, concurs to myocardial injury and may cause chronic elevation of troponin.
For outpatients with stable chest pain symptoms, there is a lack of sufficient supporting information concerning troponin testing. The expert panel does not recommend a single-test approach, which should be confined to an ED setting.
In general, the expert panel advises to have a consistent transition from one method to the other across all departments and services of an institution, following gradual and dedicated training of all personnel involved in this practice. Specific strategies should be defined and standardized, tailoring them to the specific needs of the department and institution.
Original article: J Am Coll Cardiol 2019;73:1059-1077
Author: Lorena Casadonte, Cardiology Update
