Utility of Second Troponin Measurement in Low-Risk Chest Pain
For patients with low-risk chest pain, a second troponin measurement at 1-3 hours after the initial sample for high-sensitivity troponin assays or 3-6 hours for conventional troponin assays is recommended to exclude myocardial injury. 1
Risk Stratification and Troponin Testing Protocol
- Patients presenting with acute chest pain should be categorized into low-, intermediate-, and high-risk strata to facilitate disposition and subsequent diagnostic evaluation 1
- For patients deemed low-risk (<1% 30-day risk of death or major adverse cardiovascular events), discharge home without admission or urgent cardiac testing is reasonable 1
- For intermediate-risk patients, management in an observation unit is reasonable to shorten length of stay and lower cost relative to inpatient admission 1
Timing of Serial Troponin Measurements
- For high-sensitivity troponin assays: 1-3 hours after initial sample collection 1
- For conventional troponin assays: 3-6 hours after initial sample collection 1
- Institutions should implement a clinical decision pathway that includes a protocol for troponin sampling based on their particular assay 1
Special Considerations for High-Sensitivity Troponin
- For patients with acute chest pain, a normal ECG, and symptoms that began at least 3 hours before ED arrival, a single high-sensitivity troponin concentration below the limit of detection on initial measurement may be reasonable to exclude myocardial injury 1
- High-sensitivity troponin T assay at the cut-off point of the 99th percentile has been shown to be highly sensitive for the diagnosis of myocardial infarction by two hours after presentation 2
- The sensitivity of high-sensitivity troponin assays reaches 100% among patients who present four to six hours after symptom onset 2
Diagnostic Performance of Serial Troponin Testing
- Combining the 99th percentile cutoff at admission with the serial change in troponin concentration within 3 hours significantly increases the positive predictive value for ruling in acute myocardial infarction 3
- For high-sensitivity troponin I, the positive predictive value increases from 75.1% at admission to 95.8% after 3 hours 3
- For conventional troponin I, the positive predictive value increases from 80.9% at admission to 96.1% after 3 hours 3
- Using levels obtained at 3 hours after admission, both high-sensitivity and conventional troponin assays achieve a sensitivity of 98.2% and a negative predictive value of 99.4% 3
Prognostic Value of Troponin Testing
- Any detectable elevation of troponin identifies patients at high risk for ischemic complications 1
- The risk of complications increases proportionally with the absolute level of troponin 1, 4
- Patients with elevated troponin derive greater benefit from treatment with platelet glycoprotein IIb/IIIa inhibitors, low-molecular-weight heparin, and early percutaneous coronary intervention than those without elevated troponin levels 1, 4
- Even small increases in high-sensitivity troponin indicate increased risk for death or myocardial infarction during follow-up 5
- Risk is highest in chest pain patients with dynamic changes of high-sensitivity troponin levels >30% 5
Common Pitfalls and Caveats
- A normal level of troponin on ED presentation, particularly within 6 hours of chest pain onset, does not exclude myocardial infarction 1
- Elevated troponin is indicative of cardiac injury but not necessarily ischemic cardiac injury - consider alternative causes such as myocarditis, pulmonary embolism, or heart failure 1, 4
- In patients with borderline elevated troponin levels, obtain a careful clinical history before administering potent antithrombin and antiplatelet agents that can cause bleeding 1, 4
- Previous cardiac testing, when available, should be considered and incorporated into clinical decision pathways 1
- The best predictive accuracy for elevated troponin occurs with the use of the 99th percentile of the normal value 1, 4