Tests for epilepsy

Blood tests, an Electroencephalogram (EEG) and scans are used to gather information for a diagnosis. Tests on their own cannot confirm or rule out epilepsy.

Reasons for tests

Your neurologist or specialist may ask you to have some tests to get extra information about your seizures. The tests are usually done by a technician (a person who is trained to do them).

The results from the tests are then passed back to the neurologist to see what they show. The results may indicate that you have epilepsy and may also show a cause for your epilepsy.

No test can say for certain that you do or do not have epilepsy. But when the information from the tests is added to the description of what happens during your seizures, this builds up a clearer picture of what happened. This can help with the diagnosis and when choosing treatment.

There are a number of tests that can help rule out other causes. These include:

Blood tests

A sample of blood will usually be taken from your arm with a syringe. The sample is used to check your general health and to rule out other possible causes for your seizures, such as low blood sugar levels or diabetes.

Electrocardiogram (ECG)

An ECG is used to record the electrical activity of the heart. This is done by sticking electrodes (a bit like plasters) to the arms, legs and chest. These electrodes pick up the electrical signals from the heart.

An ECG does not give out electrical signals, so having one doesn’t hurt. An ECG can help to rule out the seizure being caused by the way the heart is working.

Electroencephalogram (EEG)

An EEG is used to record the electrical activity of the brain by picking up electrical signals from the brain cells. 

Brain scans

A brain scan may help to find the cause of your seizures. The scan produces pictures of the brain which might show a physical cause for epilepsy, such as a scar on the brain. But for many people a brain scan does not show up a cause for their seizures, and even if no physical cause is seen, the person may still have epilepsy.

The two common types of brain scan are Magnetic Resonance Imaging (MRI) and Computerised Axial Tomography (CT or CAT).

Magnetic Resonance Imaging (MRI)

An MRI scan looks at the structure of the brain and may help to find the cause of your epilepsy.

Computerised Axial Tomography (CT or CAT) scan

Some people may have a CT scan if they are not able to have an MRI scan (for example, if they have a heart pacemaker, if they might need to have an anaesthetic to have an MRI, or if information about what might be causing their seizures is needed quickly). 

CT scans use X-rays to take images of the brain. CT scans are not suitable if you are pregnant because the X-rays could affect an unborn baby.

Images from a CT scan are less detailed than those from MRI scans. During a CT scan you lie on a couch which slides into the scanner. Unlike MRI scanners, CT scanners do not make a loud noise. 

Other Tests

In some situations you may also be offered genetic testing.

If the neurologist thinks that autoimmune encephalitis may have been the cause of your seizure, you may be referred for antibody testing.

Epilepsy Society is grateful to Dr F J Rugg-Gunn, Consultant Neurologist & Honorary Associate Professor, Clinical Lead, Chalfont Centre for Epilepsy, who reviewed this information.

Information updated: February 2024