Recognising Stroke: The FAST Test That Saves Lives

Two million brain cells per minute

That is the number neurologists quote — and it is not an exaggeration. During an ischemic stroke, a clot blocks blood flow to part of the brain, and oxygen-starved neurons begin to die almost immediately. For every minute that treatment is delayed, an estimated 1.9 million brain cells are lost.

The single most important variable in stroke recovery is how quickly the person gets to a hospital. Clot-busting medication (tPA) only works within a 4.5-hour window from symptom onset. Mechanical thrombectomy — physically removing the clot — works within roughly 24 hours, but the earlier the better. After that, the damage is largely permanent.

And the most common consequence of untreated stroke in the left hemisphere? Aphasia.

What FAST stands for

FAST is the most widely taught stroke recognition tool in the world, endorsed by the American Stroke Association, the NHS, and stroke foundations across more than 40 countries. It works because it captures the three most common stroke symptoms in a sequence anyone can remember.

Photo: Unsplash

Beyond FAST: the less obvious signs

FAST catches roughly 88% of strokes, but it misses about 1 in 10 — particularly strokes affecting the back of the brain (posterior circulation strokes). Several stroke organisations now teach the expanded BE-FAST acronym to cover these:

• ·Balance — sudden loss of coordination, dizziness, or difficulty walking
• ·Eyes — sudden vision loss in one or both eyes, double vision, or blurred vision
• ·Face droop, Arm weakness, Speech difficulty (as above)
• ·Time to call emergency services

Other warning signs include sudden severe headache without an obvious cause, sudden confusion, or unexplained nausea and vomiting. If something feels wrong and you are not sure, call anyway. Emergency dispatchers would rather respond to a false alarm than miss a stroke.

What happens when you call

The moment you call emergency services, a chain of events begins. The dispatcher will likely ask the same FAST questions you just answered. Paramedics, on the way, will conduct a more detailed pre-hospital stroke screen and radio ahead to the receiving hospital. Many regions now operate stroke alerts — the emergency department, CT suite, and neurology team are all activated before the ambulance arrives.

On arrival, the patient typically goes straight to imaging. A CT scan within minutes determines whether the stroke is ischemic (clot) or hemorrhagic (bleed) — these require opposite treatments. From there, if eligible, clot-busting drugs or thrombectomy can be performed within the critical window.

Why we built FAST Check into AphaSay

AphaSay is primarily a recovery tool — pairing AI speech reconstruction with a daily home practice routine — but stroke survivors and their families are also one of the highest-risk groups for a second stroke. About 1 in 4 stroke survivors experience another stroke within five years. That is why the app includes a guided FAST Check feature: a 3-step assessment with live face-tracking, arm-drift detection, and a speech sample, all in under a minute. (You can see the full feature list here.)

It is not a replacement for emergency services. It is a tool that helps caregivers and patients catch the warning signs earlier, especially in the night-time and early-morning hours when stroke incidence peaks and a partner may not be sure whether to call. For caregivers in this situation, our guide to supporting someone with aphasia covers what comes after the emergency.