Testing for stroke starts the moment symptoms appear and happens in stages: a quick physical check anyone can perform, followed by brain imaging and blood tests in the emergency room. Speed matters more than almost anything else because clot-dissolving treatment works best within 4.5 hours of symptom onset, and clot-removal procedures have their own time limits. Knowing what each stage looks like can help you act faster if you or someone near you shows warning signs.
The First Test: Spotting Stroke Signs Yourself
Before any hospital equipment gets involved, the most important “test” is recognizing symptoms and calling 911. The acronym BE FAST walks you through what to check:
- B, Balance: Sudden loss of balance or coordination.
- E, Eyes: Sudden blurred or double vision, or vision loss in one or both eyes.
- F, Face: Ask the person to smile. Does one side of the face droop?
- A, Arms: Ask them to raise both arms. Does one drift downward?
- S, Speech: Ask them to repeat a simple sentence like “The sky is blue.” Is their speech slurred or hard to understand?
- T, Time: If any of these signs are present, call 911 immediately.
Even if symptoms disappear after a few minutes, that still warrants an emergency call. A transient ischemic attack (TIA), sometimes called a “mini-stroke,” produces the same signs but resolves on its own. It’s a major warning: patients who present with all five risk factors (older age, high blood pressure, weakness, speech problems, and diabetes) have an estimated 34% chance of a full stroke in the near future.
What Paramedics Check on the Way to the Hospital
EMS crews use a streamlined version of the same physical exam. The Cincinnati Prehospital Stroke Scale evaluates three things: facial paralysis, arm weakness, and speech abnormalities. It takes under a minute and helps paramedics alert the hospital to prepare the stroke team before the ambulance arrives. That head start can shave critical minutes off the time to treatment.
Some regions now deploy mobile stroke units, which are ambulances equipped with a CT scanner. Current American Heart Association guidelines endorse these units because they allow brain imaging to begin before a patient even reaches the emergency department.
Brain Imaging in the Emergency Room
The first hospital test is almost always a non-contrast CT scan of the head. It takes only minutes and answers the single most urgent question: is this a stroke caused by a blood clot (ischemic) or by bleeding in the brain (hemorrhagic)? The answer determines everything about treatment, because clot-dissolving drugs would be dangerous in a bleeding stroke.
CT is fast, widely available, and reliable at detecting bleeding. Its weakness is sensitivity to early ischemic damage. In the first several hours, a standard CT scan can appear normal even when a clot is blocking blood flow. Subtle signs like a faint loss of contrast between gray and white matter or a bright spot in an artery (the “hyperdense vessel sign”) can hint at ischemia, but they’re easy to miss.
MRI is significantly more sensitive and specific for detecting ischemic stroke. A specialized MRI technique called diffusion-weighted imaging can reveal areas of damaged brain tissue within minutes of the event, at a stage when CT is still negative. MRI is also better at identifying stroke mimics, conditions that look like stroke but aren’t. The tradeoff is time: MRI takes longer, isn’t available in every emergency department, and can’t be used on patients with certain metal implants or who are too unstable to lie still.
CT Angiography and Perfusion Imaging
If the initial CT suggests an ischemic stroke, most stroke centers add two more scans in the same session. Together, the full protocol (plain CT, CT angiography, and CT perfusion) requires only about two minutes of additional scanning time beyond the initial scan.
CT angiography maps the blood vessels from the aortic arch up through the brain. Its primary job is locating a large vessel occlusion, a clot blocking one of the brain’s major arteries. Finding that clot is essential because it determines whether a patient is a candidate for mechanical thrombectomy, a procedure where doctors physically retrieve the clot using a catheter.
CT perfusion goes a step further. It measures blood flow through different regions of the brain to distinguish tissue that is already dead (the infarct core) from tissue that is starved but still salvageable (the penumbra). When there’s a large mismatch between those two zones, meaning lots of brain tissue can still be saved, the case for thrombectomy is strongest. This imaging has expanded treatment eligibility for patients who arrive outside the traditional time windows.
Blood Tests During Stroke Evaluation
While imaging is the centerpiece of stroke diagnosis, blood work runs in parallel. A blood glucose check is one of the very first tests performed because extremely low blood sugar can mimic stroke symptoms almost perfectly. If glucose is the problem, correcting it resolves the “stroke” without any further treatment.
Coagulation studies measure how quickly your blood clots. These results are essential before administering clot-dissolving medication, since giving it to someone whose blood already doesn’t clot well could cause dangerous bleeding. A complete blood count, kidney function tests, and cardiac biomarkers round out the standard panel. None of these diagnose stroke directly, but they rule out mimics and flag conditions that change which treatments are safe.
Ruling Out Stroke Mimics
Nearly one-third of patients who arrive at the emergency department with sudden neurological symptoms turn out to have something other than a stroke. The most common mimics include seizures, migraines (especially migraine aura without headache), brain tumors, and metabolic problems like low blood sugar or electrolyte imbalances. Less common mimics include infections, fainting episodes, and conversion disorder.
Migraine aura, in particular, can be tricky. It sometimes causes one-sided weakness or speech difficulty that looks exactly like a stroke. Clues that point toward migraine include a history of migraines, symptoms that don’t follow the pattern of a single blocked artery, and the absence of a large vessel occlusion on imaging. MRI with perfusion imaging is the most reliable way to tell the two apart, since migraine-related blood flow changes typically spread across multiple vascular territories rather than staying confined to one.
The Neurological Exam: Measuring Severity
Once a stroke is confirmed, the medical team uses the NIH Stroke Scale to quantify how severe it is. This standardized exam scores 11 categories of neurological function, including level of consciousness, eye movements, visual fields, facial strength, arm and leg strength, coordination, sensation, language, and speech clarity. Each category gets a numerical score, and the total indicates whether the stroke is mild, moderate, or severe.
The score isn’t just academic. It directly influences treatment decisions and helps predict outcomes. It’s also repeated over time to track whether a patient is improving or worsening, which can trigger changes in the treatment plan.
Tests After the Emergency: Finding the Cause
Once the immediate crisis is managed, a second round of testing looks for the underlying cause to prevent another stroke. The standard workup includes several components.
Carotid ultrasound (also called duplex sonography) examines the arteries in the neck for narrowing or plaque buildup. This is one of the most common identifiable causes of ischemic stroke, and finding significant blockage can lead to a procedure to open or bypass the artery.
Echocardiography checks the heart for conditions that could send clots to the brain. A standard transthoracic echocardiogram (an ultrasound probe on the chest) can detect blood clots in the heart chambers, valve disease, and structural abnormalities. A transesophageal echocardiogram, performed with a probe passed down the throat, gives a clearer view of the left atrium, the aortic arch, and the wall between the heart’s upper chambers. It’s better at finding a patent foramen ovale, a small hole between the heart’s chambers that can allow clots to cross into the brain’s circulation.
Heart rhythm monitoring lasts at least 24 hours and often longer. Atrial fibrillation, an irregular heart rhythm, is a major stroke risk factor that can be intermittent and easy to miss on a single ECG. Extended monitoring with a portable device catches episodes that a brief recording in the emergency department would not.
These post-stroke tests shape long-term prevention. A patient whose stroke was caused by atrial fibrillation, for example, will typically start long-term blood-thinning medication, while someone with severe carotid narrowing may need a surgical or catheter-based procedure to open the artery.