When should one or two troponin (cardiac biomarker) tests be ordered in the emergency department for acute coronary syndrome (ACS) workup?

Troponin Testing Protocol for ACS Workup in the Emergency Department

For patients presenting with suspected ACS in the emergency department, two troponin measurements should be obtained: an initial troponin upon arrival and a second troponin between 6-12 hours after symptom onset if the initial troponin is negative.

Timing of Troponin Testing

Initial Troponin Testing

• All patients presenting to the ED with symptoms suspicious of cardiac ischemia should have cardiac biomarker testing as part of initial evaluation 1
• A cardiac-specific troponin is the preferred biomarker and should be measured immediately upon admission 1
• Results should be obtained within 60 minutes of blood sampling 1

Second Troponin Testing

• For patients who present within 6 hours of symptom onset with a negative initial troponin, a second troponin should be measured between 6-12 hours after symptom onset 1
• This timing accounts for the release kinetics of troponin, which may not be detectable in the very early phase of myocardial injury 2

Special Considerations

High-Sensitivity Troponin Assays

• When high-sensitivity troponin assays are available, accelerated protocols may be considered:
  • 0h/1h algorithm with blood sampling at 0h and 1h 1
  • 0h/2h algorithm with blood sampling at 0h and 2h 1
  • These protocols can identify low-risk patients more rapidly but require validated high-sensitivity assays

Risk Stratification

• For patients with negative troponins, risk stratification tools should be used to guide further management:
  • HEART score (History, ECG, Age, Risk factors, Troponin) 1
  • TIMI (Thrombolysis in Myocardial Infarction) score 1
• Low-risk patients (e.g., HEART score <3) with negative serial troponins may be safely discharged 1

Common Pitfalls to Avoid

1. Single Troponin Testing Limitations:

   • A single negative troponin does not rule out ACS, particularly in early presenters 1
   • Although some studies suggest safety of single troponin testing in selected low-risk patients 3, guidelines consistently recommend serial testing for optimal sensitivity

2. Timing Errors:

   • Testing too early after symptom onset can miss rising troponin levels
   • The sensitivity of troponin is lower within the first 6 hours of symptom onset 2

3. Assay Considerations:

   • Different troponin assays have varying sensitivities and specificities 4
   • Point-of-care troponin testing may have lower sensitivity than central laboratory testing 1

Special Populations

• High-Risk Patients: Even with negative troponins, patients with concerning clinical features or ECG changes may require additional evaluation or admission
• Late Presenters: For patients presenting >12 hours after symptom onset, a single troponin may be sufficient if negative, but clinical judgment should prevail

Conclusion

The two-troponin approach (initial and 6-12 hours after symptom onset) remains the standard for ACS evaluation in the emergency department, balancing diagnostic accuracy with resource utilization. High-sensitivity assays may allow for shorter intervals between measurements, but the principle of serial testing remains important for optimal patient safety.