Which examinations are required to classify an acute ischemic stroke according to the TOAST (Trial of ORG 10172 in Acute Stroke Treatment) criteria?

TOAST Classification Examinations for Acute Ischemic Stroke

To classify an ischemic stroke using the TOAST criteria, you must obtain brain imaging (CT or MRI), vascular imaging of cervical and intracranial vessels, cardiac evaluation (ECG, echocardiography, and rhythm monitoring), and basic laboratory tests including complete blood count, coagulation studies, and metabolic panel. 1

Essential Diagnostic Studies

Brain Imaging (Mandatory)

• Non-contrast CT or MRI is required to confirm ischemic stroke and exclude hemorrhage 2
• MRI with diffusion-weighted imaging (DWI) is preferred when available, as it detects infarction in approximately 40% of patients even with transient symptoms and helps identify infarct patterns (scattered emboli versus single territory involvement) 3, 4
• Brain imaging must be completed urgently—ideally within 25 minutes of emergency department arrival for potential thrombolytic candidates 3

Vascular Imaging (Required for Subtype Classification)

• Cervical and intracranial vessel imaging is essential to identify large-artery atherosclerosis (≥50% stenosis) versus normal vessels 2
• Options include: CT angiography (CTA), MR angiography (MRA), carotid duplex ultrasound, or transcranial Doppler 2
• This distinguishes large-artery atherosclerosis from cardioembolic or small-vessel disease 1

Cardiac Evaluation (Required for Subtype Classification)

• 12-lead ECG to detect atrial fibrillation and other arrhythmias 2
• Cardiac rhythm monitoring (telemetry or Holter) to identify paroxysmal atrial fibrillation 2
• Echocardiography (transthoracic ± transesophageal) to identify cardiac sources of embolism—performed in 92% of patients in clinical practice 5
• Cardiac biomarkers (troponin preferred) to assess for concurrent myocardial ischemia 2

Laboratory Tests (Routine)

• Complete blood count with platelet count 2
• Prothrombin time/INR and activated partial thromboplastin time 2
• Serum electrolytes and renal function 2
• Blood glucose (to exclude hypoglycemic mimics) 2
• Fasting lipid profile 2
• Erythrocyte sedimentation rate and/or C-reactive protein 2

Selected Additional Studies (When Indicated)

• Transcranial Doppler with emboli detection may help differentiate embolic from thrombotic mechanisms (performed in 51% of patients in specialized centers) 5
• Toxicology screen and blood alcohol level if history uncertain 2
• Prothrombotic screening in young patients or those with unexplained stroke 2
• Lumbar puncture only if subarachnoid hemorrhage suspected and CT negative 2

TOAST Classification Framework

The TOAST system categorizes strokes into five subtypes based on these diagnostic findings 1:

1. Large-artery atherosclerosis: Requires evidence of ≥50% stenosis or occlusion of major brain artery on vascular imaging 2, 1
2. Cardioembolism: Requires identification of high-risk cardiac source on ECG, rhythm monitoring, or echocardiography 2, 1
3. Small-vessel occlusion (lacunar): Diagnosed with small (<1.5 cm) deep infarct on imaging and absence of large-artery stenosis or cardiac source 2, 1
4. Other determined etiology: Requires specific diagnostic tests (e.g., vasculitis screen, hypercoagulable workup) based on clinical suspicion 1
5. Undetermined etiology: Assigned when workup is incomplete, multiple potential causes exist, or no cause identified despite complete evaluation 1

Critical Pitfalls to Avoid

• Do not attempt to classify stroke subtype based solely on clinical features—initial clinical impression agrees with final diagnosis in only 62% of cases 6
• Do not restrict diagnostic workup based on presumed subtype—all patients require comprehensive evaluation regardless of initial clinical impression 6
• Do not delay thrombolytic therapy while awaiting coagulation studies unless there is clinical suspicion of bleeding abnormality or known anticoagulant use 2
• Recognize that approximately 15-25% of strokes remain undetermined despite complete evaluation, and up to 39% may be misclassified in routine clinical practice 6, 5

Timing Considerations

All diagnostic studies should be obtained as part of the acute stroke evaluation, with brain imaging and basic laboratory tests performed emergently 2. Vascular and cardiac imaging should be completed during the initial hospitalization to allow accurate TOAST classification at discharge 1, 5. Extended cardiac monitoring beyond 24 hours significantly increases detection of occult atrial fibrillation 4.