From the Guidelines
After a cardiac arrest, essential laboratory tests should include arterial blood gases, complete blood count, comprehensive metabolic panel, cardiac biomarkers (troponin, CK-MB), coagulation studies (PT/INR, PTT), and lactate levels, as recommended by the 2015 American Heart Association guidelines update for cardiopulmonary resuscitation and emergency cardiovascular care 1. These tests help assess oxygenation status, acid-base balance, organ function, cardiac damage, and tissue perfusion.
- Additional important tests include:
- Toxicology screening if overdose is suspected
- Thyroid function tests
- Blood cultures if infection is a concern
- Arterial blood gases provide immediate information about oxygenation and acid-base status, which guides ventilation management.
- Cardiac biomarkers help determine if myocardial infarction precipitated the arrest.
- Electrolyte abnormalities, particularly potassium, calcium, and magnesium, can trigger arrhythmias and should be promptly identified and corrected.
- Lactate levels serve as a marker of tissue hypoperfusion and can help track response to resuscitation efforts.
- Renal and liver function tests assess end-organ damage from hypoperfusion. These laboratory tests should be obtained as soon as possible after return of spontaneous circulation to guide immediate post-arrest management and identify reversible causes of the arrest, as supported by the 2015 guidelines update 1 and other studies 1.
From the Research
Laboratory Tests After Cardiac Arrest
The following laboratory tests should be considered after a cardiac arrest:
- Cardiac troponin to evaluate for ischemic etiology, although its utility is limited 2
- Electrolyte panel to assess for disturbances such as hypokalemia, hyperkalemia, and hypomagnesemia 3
- Blood glucose to evaluate for dysglycemia 3
- Lactate levels to assess for metabolic acidosis 3
- Complete blood count and coagulation studies to evaluate for potential bleeding or thrombotic complications
- Arterial blood gas to assess for respiratory acidosis or alkalosis
Rationale for Laboratory Tests
These laboratory tests are important to identify underlying causes of cardiac arrest, such as acute coronary syndrome, and to guide management of post-cardiac arrest syndrome 4. Additionally, laboratory tests can help identify metabolic and electrolyte disturbances that may have contributed to the cardiac arrest and guide correction of these abnormalities 3.
Limitations of Laboratory Tests
It is essential to note that while laboratory tests can provide valuable information, they should be interpreted in the context of the patient's clinical presentation and other diagnostic findings. For example, cardiac troponin may not be a reliable marker for ischemic etiology or left ventricular systolic dysfunction in the post-cardiac arrest setting 2.