Testing for seizures involves a combination of brain wave recordings, brain imaging, blood work, and detailed observation of what happens before, during, and after an episode. No single test can definitively confirm or rule out seizures in every case, so doctors typically use several tools together to build a complete picture.
EEG: The Core Test for Seizure Activity
An electroencephalogram, or EEG, is the primary test used to evaluate seizures. Small electrodes are placed on your scalp to record the electrical activity in your brain. Doctors look for abnormal patterns, such as spikes or sharp waves, that indicate a tendency toward seizures. A routine EEG takes about 20 to 30 minutes and is painless.
The catch with a routine EEG is that it only captures a brief snapshot. If your brain isn’t producing abnormal signals during that narrow window, the test can come back normal even if you do have epilepsy. That’s why a normal EEG doesn’t rule seizures out, and an abnormal one doesn’t always mean you’ll have seizures in the future. It’s one piece of evidence, not a verdict.
Video EEG Monitoring
When a routine EEG isn’t enough, doctors may recommend video EEG monitoring, which records both your brain activity and your physical movements on camera simultaneously. This is typically done in a hospital epilepsy monitoring unit, where you stay connected to the equipment around the clock. The goal is to actually capture an episode on record so doctors can see exactly what your brain is doing while it happens.
A video EEG stay can last anywhere from a few days to a week or more, depending on how frequently your seizures occur. This test is especially useful for determining whether unusual episodes are truly epileptic seizures, identifying the specific type of seizure you’re having (such as absence seizures, which can look like brief staring spells), and pinpointing which region of the brain the seizures originate from. That last point matters a great deal if surgery ever becomes part of the conversation.
Ambulatory EEG: Testing at Home
An ambulatory EEG lets you go about your normal life while wearing a portable recording device for 24 to 72 hours. You keep a diary of your activities, sleep, and any symptoms you notice. Most recorders also have an event button you can press if you feel a seizure or unusual sensation coming on, which marks that moment in the recording for your doctor to review.
This approach captures far more brain activity than a 20-to-40-minute routine EEG, which increases the chance of catching abnormal patterns. It’s particularly helpful when seizures happen infrequently or are triggered by everyday situations that can’t be replicated in a clinic.
Brain Imaging With MRI and CT
Imaging tests look at the brain’s structure rather than its electrical activity. An MRI produces detailed images that can reveal tumors, scar tissue, blood vessel abnormalities, or areas of abnormal brain development that might be causing seizures. It’s the preferred imaging test for most people being evaluated for epilepsy because of its high level of detail.
A CT scan is faster and more widely available, so it’s often the first imaging test used in an emergency room after a first-time seizure. It’s good at detecting bleeding, large masses, or strokes but doesn’t show the fine structural detail that an MRI provides. Many people end up getting both at different stages of their evaluation.
Blood Tests and Lab Work
Blood draws help doctors rule out medical conditions that can trigger seizures without any underlying brain disorder. The key things they’re checking include blood sugar levels (both very high and very low blood sugar can cause seizures), electrolyte imbalances (the salts your body uses to regulate fluid balance and nerve signaling), signs of infection, and markers of kidney or liver function. If a metabolic problem caused the seizure, treating that problem may be all that’s needed.
What Your Doctor Looks for in a Physical Exam
A neurological exam checks your reflexes, coordination, muscle strength, sensation, and mental status. Certain skin findings can point to specific conditions linked to epilepsy, such as the birthmarks seen in tuberous sclerosis or Sturge-Weber syndrome. Doctors also look for signs of past injuries, like old scars from falls or stitches, which can suggest a longer history of unrecognized seizures.
Just as important is the information you and any witnesses can provide. Doctors want to know what happened before, during, and after the episode. Specific details that matter include whether you had automatic or repetitive movements like lip smacking, chewing, hand rubbing, or picking at your clothes. Eye behavior is significant too: staring, blinking, or eyes rolling to one side. How long the episode lasted and how long it took you to feel normal afterward (the recovery period) are critical details. If someone can capture video of an episode on their phone, that recording can be one of the most valuable diagnostic tools available.
Genetic Testing
Genetic testing is recommended for anyone with epilepsy that doesn’t have a clear cause. It’s most likely to identify a diagnosis when seizures are difficult to control with medication, when other neurological symptoms are present (such as developmental delay, autism, or movement disorders), or when there’s a strong family history of epilepsy.
Epilepsy gene panels analyze anywhere from fewer than 20 to several hundred genes known to be associated with seizure disorders. Some genetic findings directly guide treatment. For example, Dravet syndrome is most often caused by a variant in the SCN1A gene, and confirming that diagnosis changes which medications are used because certain common seizure drugs can actually make Dravet syndrome worse.
How Epilepsy Is Officially Diagnosed
The International League Against Epilepsy defines epilepsy as a brain disease meeting at least one of three criteria: two or more unprovoked seizures occurring more than 24 hours apart, one unprovoked seizure with a 60% or greater probability of another seizure within the next 10 years, or a recognized epilepsy syndrome. That second criterion is where testing becomes so important. If your EEG shows clear epileptic patterns or your MRI reveals a structural abnormality known to cause seizures, your doctor may diagnose epilepsy after just one seizure because the recurrence risk is high enough.
Wearable Seizure Detection
Wearable devices are beginning to play a role in ongoing seizure monitoring. The FDA recently cleared EpiWatch, a platform developed by Johns Hopkins Medicine that runs on the Apple Watch and is designed to continuously monitor for tonic-clonic seizures (the type that causes full-body convulsions and loss of consciousness). These devices don’t replace EEGs for diagnosis, but they can help track seizure frequency over time and alert caregivers when a seizure occurs, which is especially useful for people who live alone or have seizures during sleep.