When troponin was a lousy assay it was a great test, but now that it’s becoming a great assay, it’s getting to be a lousy test.
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How good is ECG alone for diagnosis of acute myocardial infarction (AMI)? [2]
- Specificity 97%
- Sensitivity 28%
- Due to the poor sensitivity of ECGs, cardiac biomarkers are also needed.
Does an elevated high sensitivity troponin (hsTn) mean acute coronary syndrome (ACS)?
- hsTn can be found circulating in the plasma as a result of any transient ischemic or inflammatory myocardial injury, such as cardioversion, CHF, aortic dissection, HOCM, tachyarrhythmia, myocarditis/pericarditis [1]
- Non-cardiac causes of elevated hsTn include: PE, renal failure, SAH, sepsis, burns, and extreme exertion (i.e. marathons) [1]
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What should a provider do with troponin elevation from non-ACS etiologies? [3]
- Unfortunately, little data is available on management of these patients
- There is data evolving on elevated Tn levels in conditions such as CHF, PE, sepsis, and renal failure
- There is a proposed algorithm currently from the best evidence available (has not been validated):
How often is serial troponin testing needed with hsTn to rule out acute MI (every 2, 4, 6, or 8 hours)?
- 1/5 of patients with AMI will have a normal hsTn at presentation and should have repeat testing [2]
- The National Institute for Health and Clinical Excellence (NICE) Guidelines recommend measuring Tn on admission and 10 – 12 hours after the onset of symptoms (This needs to be updated, due to current use of hsTn testing) [2]
- Most recent guidelines from Global Task Force state Tn testing should be obtained at admission and at 3 – 6 hours after admission, irrespective of the timing of the onset of symptoms [2]
- Lower sensitivity Tn requires at least 6 hours between time of initial lab and repeat Tn to see a conclusive increase to rule in AMI [1]
- High sensitivity Tn requires only 2 to 3 hours between time of initial lab and repeat Tn to see a conclusive increase to rule in AMI [1]
- A normal hsTn at 3 hours has a NPV of 99% in excluding AMI [1]
- Dr Louise Cullen et al have recently published a paper: [4]
- 1,635 patients with 30 day follow up for Major Adverse Cardiac Events (MACE)
- Non-ischemic ECG, TIMI of 0, and negative hsTn (0 and 2 hours): 0% MACE with Sens 100%, Spec 23.1%, NPV 100%
- Non-ischemic ECG, TIMI of ≤1, and negative hsTn (0 and 2 hours): 0.8% MACE with Sens 99.2%, Spec 48.7%, and NPV 99.7%
- Conclusion: Early discharge strategy utilizing a hsTn assay, TIMI ≤1, and non-ischemic ECG can safely decrease observation periods and admissions in approximately 40% of patients with suspected ACS
- Current best EBM: Serial sampling of hsTn at 0 and 2 hours is essential to permit the safe rule-out of AMI and to minimize misdiagnosis in patients with elevated hsTn (Another case of guidelines being behind)
What is considered a “significant change” in hsTn levels? [1]
- According to the European Society of Cardiology (ESC):
- Increase of ≥20% if first Tn elevated, or
- Increase of ≥50% in patients with small initial Tn elevations
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Conclusion
hsTn is the preferred biomarker for the diagnosis of AMI, but remember that conditions other than AMI may cause acute and chronic elevations.
References:
- Mahajan VS et al How to Interpret Elevated Cardiac Troponin Levels. Circulation 2011. PMID: 22105197
- Shah AS et al. High Sensitivity Cardiac Troponin in Patients with Chest Pain. BMJ 2013. PMID: 23878152
- de Lemos JA et al. Increasingly Sensitive Assays for Cardiac troponins: A Review. JAMA 2013. PMID: 23736735
- Cullen L et al. Validation of High-Sensitivity Troponin I in a 2-Hour Diagnostic Strategy to Assess 30-Day Outcomes in Emergency Department Patients with Possible Acute Coronary Syndrome. JACC 2013. PMID: 23583250
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