From the Guidelines
When evaluating a patient with chest pain, the most critical laboratory tests to order promptly include cardiac biomarkers, such as high-sensitivity troponin, with serial measurements at 0,3, and 6 hours, as recommended by the 2021 AHA/ACC/ASE/CHEST/SAEM/SCCT/SCMR guideline 1. These tests are crucial for diagnosing myocardial infarction and guiding treatment decisions.
Key Laboratory Tests
- Cardiac biomarkers (troponin I or T, preferably high-sensitivity troponin) with serial measurements at 0,3, and 6 hours
- Complete blood count (CBC) to identify anemia or infection
- Comprehensive metabolic panel (CMP) to assess electrolytes and renal function
- Brain natriuretic peptide (BNP or NT-proBNP) to evaluate for heart failure
- Coagulation studies (PT/INR, PTT, and D-dimer) when pulmonary embolism is suspected
Rationale
The 2021 guideline emphasizes the importance of prompt measurement of cardiac troponin (cTn) in patients with acute chest pain and suspected acute coronary syndrome (ACS) 1. Serial troponin levels should be obtained at presentation and 3 to 6 hours after symptom onset to identify a rising and/or falling pattern of values, as recommended by the 2014 AHA/ACC guideline 1. Additional tests, such as CRP and ESR, may be considered if inflammatory conditions are suspected.
Clinical Considerations
- An ECG should be acquired and reviewed for ST-segment–elevation myocardial infarction (STEMI) within 10 minutes of arrival, as recommended by the 2021 guideline 1
- Clinical assessment, ECG findings, and imaging studies should be combined with laboratory tests to provide a comprehensive evaluation and guide appropriate management.
From the Research
Labs to Collect with Chest Pain
The following labs are recommended to collect when a patient presents with chest pain:
- Complete Blood Count (CBC) parameters, such as total white blood cell count, neutrophil count, red cell distribution width, and neutrophil-to-lymphocyte ratio, as they may provide some clues when predicting troponin elevation 2
- Troponin levels, specifically troponin T (cTnT) or troponin I (cTnI), as they are highly cardiac-specific and can help diagnose acute myocardial infarction (AMI) 3, 4
- Myoglobin, as it can be used as a rapid marker for early diagnosis of AMI, but requires supplementation with other analyses such as troponins to support the myoglobin value 4
- CK-MB mass, as it can be used to diagnose cardiac muscle damage, but is not as specific as troponins 4
- D-dimer assay, to help determine the risk of pulmonary embolism 5, 6
- Brain natriuretic peptide level measurement, to help clarify the diagnosis of heart failure 5
- Electrocardiogram (ECG) and chest radiograph, as they are essential for evaluating patients with chest pain 5, 6
Timing of Lab Collection
The timing of lab collection is crucial, as troponin levels may not be elevated until 4-6 hours after the onset of chest pain 4. Therefore, it is recommended to collect labs at admission, and then 4-6 and 12 hours later 4.
Combination of Labs
Combining different labs can improve the diagnostic accuracy, such as combining white blood cell count, red cell distribution width, and neutrophil-to-lymphocyte ratio to predict troponin elevation 2. However, none of these combinations have sufficiently good diagnostic test criteria results to safely predict non-ST segment elevation myocardial infarction.