What labs are recommended to diagnose acute ischemic stroke?

Laboratory Tests for Diagnosing Acute Ischemic Stroke

The diagnosis of acute ischemic stroke requires both neuroimaging and laboratory tests, with essential laboratory studies including blood glucose, oxygen saturation, serum electrolytes/renal function tests, complete blood count, cardiac biomarkers, and coagulation studies (PT/INR and aPTT). 1

Essential Laboratory Tests for All Patients

• Blood glucose: Critical to exclude hypoglycemia which can mimic stroke symptoms
• Oxygen saturation: To assess respiratory status
• Serum electrolytes/renal function tests: To evaluate metabolic abnormalities
• Complete blood count (CBC): To identify anemia, thrombocytopenia, or leukocytosis
• Cardiac biomarkers (troponin): To assess for concurrent cardiac events
• Coagulation studies:
  • Prothrombin time (PT)/International Normalized Ratio (INR)
  • Activated partial thromboplastin time (aPTT)

Selected Laboratory Tests (Based on Clinical Suspicion)

• Thrombin time (TT)/Ecarin clotting time (ECT): For patients suspected to be taking direct thrombin inhibitors or direct factor Xa inhibitors
• Hepatic function tests: To evaluate liver function
• Toxicology screen: If drug intoxication is suspected
• Blood alcohol level: If alcohol intoxication is suspected
• Pregnancy test: For women of childbearing age
• Arterial blood gas: If hypoxia is suspected
• Lipid profile and HbA1c: Should be obtained within 48 hours for risk stratification 1

Important Considerations for Laboratory Testing

1. Do not delay thrombolytic therapy while awaiting laboratory results unless:

   • Clinical suspicion of bleeding abnormality or thrombocytopenia
   • Patient has received heparin or warfarin
   • Patient has received other anticoagulants 2

2. Timing of laboratory tests: Complete diagnostic evaluation should be completed or underway within 48 hours of stroke symptom onset 1

3. Special populations requiring additional testing:

   • Young patients (<50 years): Consider hypercoagulable testing (factor V Leiden, prothrombin gene mutation, protein C, protein S, antithrombin III levels)
   • Patients with family history of thrombosis: More extensive thrombophilia testing
   • Cryptogenic stroke: Consider antiphospholipid antibodies and lupus anticoagulant
   • When clinically indicated: Infectious disease screening (HIV, syphilis, hepatitis) 1

Imaging Requirements

While laboratory tests are essential, they must be complemented by:

• Brain imaging (CT or MRI): Immediately to confirm diagnosis and rule out hemorrhage
• Vascular imaging: CTA, MRA, or carotid ultrasound to identify stenosis
• 12-lead ECG: To screen for atrial fibrillation and other cardiac conditions
• Extended cardiac monitoring: At least 24 hours to detect paroxysmal atrial fibrillation 1

Clinical Algorithm for Laboratory Testing in Suspected Acute Ischemic Stroke

1. Obtain essential labs (glucose, CBC, electrolytes, renal function, coagulation studies, cardiac biomarkers) immediately upon presentation
2. Do not delay thrombolysis while awaiting results unless specific concerns exist
3. Complete additional targeted testing based on clinical presentation within 48 hours
4. Perform specialized testing for rare causes only when clinically indicated, not routinely
5. Consider more extensive workup for young patients, those with family history of thrombosis, or recurrent stroke

Remember that laboratory tests are just one component of stroke diagnosis, and neuroimaging remains the cornerstone for confirming acute ischemic stroke 2, 1.