Sleep Study: How It Works, Who Needs One, and How to Prepare

Among all adults in the U.S., 1 out of 3 experience sleep deprivation. In many cases this lack of sleep is due to a sleep disorder. In fact, up to 70 million Americans suffer from a sleep disorder. Sleep disorders affect more than just your sleep. They can increase your risk for conditions like heart disease, high blood pressure, and depression.

If you snore, have trouble sleeping, or you always feel tired when you wake up, you may have a sleep disorder. Your healthcare provider can order a sleep study, which will evaluate your sleep to diagnose any issues.

What is a sleep study, and how does it work? 

A sleep study (polysomnography) is an overnight test that records your body functions while you sleep. It's used to help find the cause of a sleeping problem. A sleep study always happens overnight at either a sleep lab or in your home.

Before you go to sleep, the technician will attach sensors to your body for the test. These typically include electrodes, a pulse oximeter, and an elastic band around your chest. The sensors are painless and are glued or taped to you. They report data back to the medical team about your body’s activity while you’re sleeping.

 The testing during a sleep study includes: 

• Electrocardiography (ECG): Chest sensors measure electrical impulses in the heart. This monitors the heart rate and any abnormal rhythms (arrhythmias).

• Electroencephalography (EEG): Electrodes on the scalp measure brain wave activity. This helps to figure out your stage of sleep throughout the night.

• Pulse oximetry: The pulse oximeter is a clip on your earlobe, finger, or toe that measures your blood oxygen level. This will watch for dips in oxygenation while you sleep.

• Electromyography: Electrodes on the arms and legs measure muscle contractions.  This checks for irregular movements when you’re sleeping.

• Airflow sensors and chest straps: Sensory prongs in your nose measure the airflow coming in and out. An elastic band around your chest measures how your chest moves when you breathe. This allows the medical team to calculate your respiratory rate. 

In a separate room, a technologist monitors you in several ways. As the sensors send their data, the technologist reads their output. There’s also a microphone to pick up snoring or talking during sleep. And a low-light video camera records your movements.

The data helps to understand how your breathing, activity, and movements affect your sleep.

What can a sleep study diagnose?

A sleep study can diagnose different issues you may have while sleeping. This includes trouble with your breathing or oxygen levels while you sleep. It can pick up small, extra movements that may be disturbing your sleep. Or it can detect complex actions like sleepwalking. It can also help figure out why you might be sleepy during the day even after a long period of nighttime sleep.  

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Common sleep disorders that a sleep study can detect are: 

• Sleep apnea: like obstructive sleep apnea, central sleep apnea, or sleep-related hypoventilation 

• Sleep movement disorders: like restless leg syndrome or periodic limb movement disorder 

• Hypersomnolence disorders: like narcolepsy or idiopathic hypersomnia

• Parasomnias: such as REM behavior disorder, sleepwalking, and sleeptalking

What’s the difference between a study at home and one in a sleep center?

A home study is an overnight sleep test you do in your own bed at home. Your healthcare provider will supply the equipment, and you’ll hook yourself up to the recorders and go to sleep. The data is sent electronically to your provider or when you return the equipment the next day.

While home sleep studies are more convenient, these tests are not as comprehensive. And they aren’t for everyone. Home tests are best for people who may have obstructive sleep apnea and those who are relatively healthy. 

In a sleep center, you can do different types of sleep studies. These options include: 

• Polysomnogram: This is the typical overnight sleep study. It monitors the different sleep cycles and body function.

• CPAP titration: This is to fit those who already have sleep apnea with a CPAP mask. It finds the best pressure to keep your airways open and prevent apnea episodes. 

• Split night study: This combines a sleep study and CPAP titration in one night. This is best if you can’t complete more than one overnight test.

• Multiple Sleep Latency Test: This is for people who are always sleepy and often fall asleep during the day. After the overnight study, the goal is to see how quickly you can fall asleep during the day. 

How to prepare for a sleep study

There are several things you can do to make the sleep study a more successful experience. Here are some suggestions:

• Be mindful of your diet. Don’t drink anything the afternoon of the study that may interfere with sleep. This includes alcohol and caffeinated beverages such as tea, coffee, and colas.

• Stay awake. Try to not take a nap on the day of the study. If it’s not easy for you to fall asleep, it may alter your test and results.

• Keep it simple. Don’t use hair gels, sprays, or oils. Anything greasy can make it hard for the sensors to stick to your skin. So you should also avoid lotion or cream on your body. 

• Bring what you need. Pack an overnight bag with pajamas, toiletries, and your usual nighttime medication. You can even bring a pillow if you prefer your own. 

What if you can’t sleep?

It's expected that you won’t sleep as well as you normally do at home. The rooms are designed to be very comfortable and quiet, like a hotel room. Sleep-enhancing techniques — like meditation, deep breathing, or progressive muscle relaxation — are helpful.

Almost everyone eventually falls asleep during the study. But if you don’t, the good news is you don’t need a full night’s sleep to get accurate results.

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Written by:

Jennifer L. Claves, MD

Jennifer L. Claves, MD, is a practicing board-certified internal medicine physician with over two decades of experience. She earned her medical degree from Penn State University and completed her residency and chief residency at Thomas Jefferson University Hospital in Philadelphia.

Edited by:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

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