Emergency Medicine Emergency Medicine · Neurology · High Yield

FAST — Stroke Recognition

FAST is the public-facing stroke recognition tool used in the UK and globally. It identifies the three most common presentations of anterior circulation stroke, prompting immediate 999 activation. Time to treatment is the single biggest determinant of outcome.

✦ The Mnemonic

"Face, Arms, Speech, Time — Call 999"

The four FAST components for rapid stroke recognition

F Face drooping One side of the face droops or is numb — ask the patient to smile; asymmetry is positive

A Arm weakness One arm is weak or numb — ask them to raise both arms; does one drift down?

S Speech difficulty Slurred, strange, or unable to speak or understand speech

T Time to call 999 If ANY of the above — time is brain. Call emergency services immediately

📚 Clinical Breakdown

FAST detects approximately 88% of strokes. The extended BE-FAST adds Balance (sudden loss) and Eyes (sudden visual disturbance) — improving sensitivity for posterior circulation strokes to ~95%. Posterior circulation strokes (vertebrobasilar territory) commonly present with vertigo, diplopia, ataxia, and dysphagia — features absent from FAST.

Time is brain: every minute of stroke, approximately 1.9 million neurons are lost. The thrombolysis window is 4.5 hours from symptom onset (IV alteplase); mechanical thrombectomy for large vessel occlusion can be performed up to 24 hours in selected patients. 'Last known well' time — not the time of discovery — defines the treatment window.

The ROSIER score (Recognition of Stroke in the Emergency Room) is used by clinicians in the emergency department to distinguish stroke from stroke mimics (hypoglycaemia, seizures, complex migraine, Todd's paresis). Blood glucose must always be checked immediately — hypoglycaemia is the most important mimic and is immediately reversible.

FAST sensitivity ~88% of strokes

BE-FAST sensitivity ~95% (adds Balance + Eyes)

Thrombolysis window 4.5 hours from symptom onset

Thrombectomy window Up to 24 hours for LVO in selected patients

⭐ Clinical Pearl

Hypoglycaemia is the number one stroke mimic — always check a BM immediately. A blood glucose <3.5 mmol/L causing focal neurology must be corrected before any stroke pathway is activated. Giving IV glucose to a hypoglycaemic patient can produce complete neurological recovery within minutes.

⚠ Exam Trap

TIA (transient ischaemic attack) is a stroke until proven otherwise. Symptoms that fully resolve still require same-day specialist assessment — the ABCD² score stratifies short-term stroke risk. Up to 10% of TIA patients will have a stroke within 48 hours. 'It got better' does not mean 'it can wait'.

← AVPU Scale