How Long Does an EEG Test Take
A routine EEG test usually takes about 20-30 minutes to complete, but the waiting period usually takes about an hour

An electroencephalogram (EEG) is a noninvasive, painless test that measures the brain's electrical activity. A routine EEG test usually takes about 20-30 minutes to complete, but the waiting period usually takes about an hour, including the prepping procedures before and after.

If the EEG is not standard and includes another procedure, it may take longer than an hour. The time it takes to complete an EEG test typically depends on the type of test performed.

What are different types of EEG tests?

Routine EEG (60-90 minutes)

  • When the exam begins, you must remain completely motionless with your eyes closed. This ensures that the equipment only detects brain waves and no other movements.
  • The technician may tell you to take deep breaths and show you flashing lights.

Prolonged EEG (1.5-3 hours or more)

  • This study is only done for certain individuals to capture EEG during normal awake and sleep states.
  • This study is similar to a standard EEG except that it records for more than 3 hours and can capture sleep EEG features, as well as events suspicious of a seizure.
  • You may require another appointment for an extended EEG following a standard EEG.

Ambulatory EEG (1-4 days)

  • Depending on how much information your doctor needs, an ambulatory EEG may take 1-4 days. 
  • During an ambulatory EEG, the technician will stick tiny metal discs to your scalp with glue.
  • Wires link the discs to a computer that you will bring home with you. This is carried in a pack that may be worn around the waist or over the shoulder.
  • To hide the cables and discs, the technician will wrap gauze over your head. You can conceal it by wearing a hat or scarf. During the exam, you will be given instructions on what you should and should not do.
  • The test begins as soon as you leave and continues until the discs are removed. You will be given a journal to record anything strange that occurs during the exam.
  • It is critical to include the date, time, and a brief description of any unexpected occurrences or symptoms.

Sleep-deprived EEG (depends on underlying diagnostic criteria)

  • You must be sleep-deprived for 4 hours for the test to be successful. 
  • If you regularly get 8 hours of sleep every night, you should only get 4 hours the night before the test.

Video telemetry or video EEG (more than 4 days)

  • This test is normally performed over a few days in a specially designed hospital suite. The EEG signals are wirelessly transferred to a computer.
  • The footage is captured by the computer and is monitored regularly by skilled personnel.

What conditions can be diagnosed by EEG?

An EEG provides significant information about the health and function of the brain. The test helps diagnose, monitor, and exclude medical conditions, as well as identify abnormalities in brain electrical activity that could be related to certain disorders. 

EEGs can be used to confirm or rule out a variety of diseases, including:

EEGs are most often used by neurologists, neurosurgeons, and pediatricians. It provides information mainly on brain function, but it can complement the results of other medical tests.

How is an EEG test performed?

EEG tests are performed by a registered electroencephalographic technician. The technician will explain the procedure and ask you to sit or lie down.

Your head will be measured, and at least 21 small metal discs called electrodes will be placed on the scalp using a paste. You will be asked to close your eyes and relax once the electrodes are in place. The brain signals recorded by the electrodes will be displayed as waves on the computer. The technician will sit next to you and keep an eye on the EEG machine.

You will be asked to remain still during the recording because any movement can obscure the EEG recording. You may be asked to perform simple tasks, such as opening and closing your eyes, taking deep breaths, or looking at a flashing light. When the EEG is finished, the technician will remove the electrodes with warm water.

EEG tests cause no side effects, and you will be able to drive and go about your normal activities.

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How safe are EEG tests?

EEG testing is a safe procedure that can be done in either an inpatient or outpatient setting. 

Although the test monitors your brain's electrical activity, no electrical current is introduced into your body. EEG is not the same as electroshock (electroconvulsive) therapy.

In those with seizure disorders, the flashing lights or rapid breathing (hyperventilation) required during the test may trigger seizures in rare cases. 

During the hyperventilation portion of the test, you may feel lightheaded and experience tingling in your lips and fingers for a few minutes. Some people experience a mild rash near the electrodes.

The only disadvantage of EEG is that the result resolution is not precise. Because EEG measures electrical activity near the scalp, many electrodes are attached to the head to obtain readings. It is impossible to guess which part of the body a particular electrical activity is from. As a result, diagnosing the problem takes time.

An EEG test may be combined with a positron emission tomography (PET) test to determine specific abnormalities more accurately in brain function.

What if my EEG results are abnormal?

In an emergency, your doctor may request a preliminary report from a neurologist. Usually, you will not receive your results on the same day. The recordings must first be analyzed before being sent to the doctor who requested the test. They can discuss the findings with you in a few days or weeks. 

Abnormal EEG results may indicate underlying brain conditions. Talk to your doctor about your EEG results and ask them to explain anything you do not understand. Inquire about the next steps, follow-up appointments or procedures, and any other factors that may have skewed your EEG results.

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Medically Reviewed on 10/6/2022
References
Image Source: iStock image

Electroencephalogram (EEG). https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/electroencephalogram-eeg

EEG (Electroencephalogram). https://www.webmd.com/epilepsy/guide/electroencephalogram-eeg

Electroencephalogram (EEG): About This Test. https://mydoctor.kaiserpermanente.org/mas/Images/EEG%20-%20About%20This%20Test_tcm88-154897.pdf

EEG (Electroencephalogram). https://www.dmc.org/services/neurology/holden-neurodiagnostics-lab/eeg-(electroencephalogram)