Sleep Study

What is a sleep study?

The stages of sleep range from light to deep. Each stage has aspects that can be measured. A sleep study is a number of tests recorded at the same time during sleep. The tests measure specific sleep aspects and help diagnose sleep disorders. A sleep study may also be called polysomnogram.

The basic recordings done during a sleep study may include:

  • Electroencephalography (EEG). This measures brain wave activity.
  • Electrooculogram (EOG). This measures eye movement.
  • Electromyography (EMG). This measures muscle movement.
  • Other recordings. An electrocardiogram (ECG) may be used to record electrical activity of the heart. Video recordings may also be made of you while you sleep.

Sleep studies generally take place in a sleep lab during your normal sleeping hours. The goal is to record brain and body activity that happens during sleep so that sleep disorders can be diagnosed and treated.

During a sleep study, the following may be measured:

  • Eye movement. The number of eye movements and their frequency or speed.
  • Brain activity. The electrical currents of the brain.
  • Limb movement. The number and intensity of movements.
  • Breathing patterns. The number and depth of respirations.
  • Heart rhythm. The electrical activity of the heart.
  • Oxygen saturation. The percentage of oxygen in the blood.
  • Acid/base balance of the stomach. The amount of acid secreted during sleep.
  • Sleep latency. The time it takes to fall asleep.
  • Sleep duration. The period of time a person stays asleep.
  • Sleep efficiency. The ratio of the total time asleep to the total time in bed.

You may also have the following tests. They are done during the day in the sleep lab instead of overnight.

  • Multiple sleep latency tests (MSLT) measure how long it takes to fall asleep.
  • Multiple wake tests (MWT) measure whether you can stay awake during specified times.

Doctors trained in sleep medicine assess test results to treat sleep issues. A trained sleep technician will be with you in the sleep lab during the testing period.

Why might I need a sleep study?

Common reasons for a sleep study include:

  • Snoring too much
  • Periods when you stop breathing during sleep (sleep apnea)
  • Daytime sleepiness
  • You can't sleep (insomnia)
  • You are very sleepy during the day and fall asleep without warning (narcolepsy)
  • Conditions that cause leg discomfort. These are called limb movement disorders. They include periodic limb movements of sleep (restless legs syndrome).

You may also need a sleep study if you have unusual behaviors during sleep such as sleep walking or talking, or rapid eye movement disorders.

Your healthcare provider may have other reasons to recommend a sleep study.

What are the risks of a sleep study?

There are no known risks for a sleep study other than possible skin irritation from the the electrodes that are attached to your skin.

How do I get ready for a sleep study?

  • Your healthcare provider will explain the procedure. You can ask questions.
  • You may be asked to sign a consent form. Read it carefully and ask any questions you have before signing the form.
  • You may be asked to limit your sleep before the study. For example, you may be asked to not nap.
  • Tell your healthcare provider about all prescription and over-the-counter medicines, and herbal supplements you take. Also tell your provider if you use alcohol before going to bed. Using any of these may change test results.
  • Don't have products with caffeine for several days before the testing. They may cause you to take longer to fall asleep.
  • Unless directed by your healthcare provider, you won't be able to use sedatives during the sleep study because they can change results.
  • You may need to fill out a sleep questionnaire or diary ahead of the test. Your sleep partner may also need to fill one out. Do your best to give true responses.
  • Showering before going to the sleep lab may be helpful. But don't use lotion or oil on your skin because the electrodes may not stick to the skin.
  • You may be urged to bring your own pajamas and pillow.
  • If needed, you may be able to shower and dress for work the morning after the sleep study.
  • Based on your condition, your healthcare provider may ask for other preparation.

What happens during a sleep study?

A sleep study is generally done on an outpatient basis at night. Procedures may vary based on your condition and your healthcare provider's practices.

Generally, a sleep study follows this process:

  1. You will need to remove any jewelry or other objects that may interfere with the procedure.
  2. You will change into pajamas or a hospital gown.
  3. The healthcare team will put small metal discs (electrodes) on your head and body for EEG, ECG, EOG, and EMG cables.
  4. The team will put a small clip on your finger to measure the oxygen level (pulse oximetry) in your blood. The team will also check your breathing.
  5. The temperature of the room may need to be kept at a certain level, but blankets can be added or removed as needed.
  6. Lights will be turned off and monitoring will start before you fall asleep.
  7. For multiple sleep latency testing (MSLT), short naps will be assigned at intervals.
  8. For multiple wake testing (MWT), you will be asked to try to stay awake for certain periods.
  9. When the study is done, the electrodes and other devices will be removed.

What happens after a sleep study?

You won't need any special care after a sleep study. Results may take several days. But your healthcare provider may give you other instructions after the procedure, based on your situation.

Next steps

Before you agree to the test or the procedure make sure you know:

  • The name of the test or procedure
  • The reason you are having the test or procedure
  • What results to expect and what they mean
  • The risks and benefits of the test or procedure
  • What the possible side effects or complications are
  • When and where you are to have the test or procedure
  • Who will do the test or procedure and what that person’s qualifications are
  • What would happen if you did not have the test or procedure
  • Any alternative tests or procedures to think about
  • When and how you will get the results
  • Who to call after the test or procedure if you have questions or problems
  • How much you will have to pay for the test or procedure
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