What Is An Overnight Sleep Study (Polysomnogram)?

What to expect when undergoing this test

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A sleep study, formally known as a polysomnogram, is performed to diagnose sleep disorders such as sleep apnea, insomnia, and restless leg syndrome (RLS). It involves spending the night at a sleep laboratory that's part of a hospital or an outpatient sleep clinic. As you sleep, electrodes attached to your head and body monitor your brain waves, breathing, and movement. A technician watches as you sleep via a discreet camera.

It can be unsettling to sleep somewhere other than your own bed and know that you're being monitored and observed. So it's natural that you may feel some anxiety about the experience. The more you understand about why the study is important and what to expect, the more comfortable you may feel.

This article explains the purpose of a sleep study, how to prepare for one, what happens during the study, how the results are interpreted, and what might come next.

sleep study setup

Verywell / Emily Roberts

Purpose of Study

Your healthcare provider may want you to undergo a sleep study if you have trouble falling asleep, wake up frequently, snore, or have other symptoms of a sleep disorder. A polysomnogram might also be advisable based on a screening test for narcolepsy (excessive daytime sleepiness). The test is known as the Epworth Sleepiness Scale.

Sleep studies are designed to diagnose sleep disorders, including:

  • Circadian rhythm disorders
  • Excessive daytime sleepiness
  • Insomnia
  • Narcolepsy
  • Parasomnias (sleep behaviors)
  • Periodic limb movements
  • Sleep apnea (a total obstruction of breathing that lasts for more than 10 seconds)

Some physicians ask their patients to write a "self-report" that summarizes their sleep issues. These reports may be helpful—to a point—but they don't always paint a reliable picture about one's sleep. This is when a sleep study often enters the picture, on the advice of the physician.

The study can paint a more complete picture about the quality of your rest and what may be going on in your body to affect it. The electrodes—small metal discs with wires attached—placed on your body monitor your brainwave activity and sleep stages, heart rhythm, muscle tone, leg movements, breathing patterns, and blood's oxygen levels. A physician then interprets all the data that is collected.

Costs Matter

As receptive as they may be to the idea of undergoing a sleep study, many patients are nervous about the cost. And it can vary. Ultimately, the cost "depends on the type of testing being used and what a facility charges. Small clinics typically charge less compared to big hospital systems." Contact the sleep study clinic or lab for a cost estimate. Then contact your health insurance company to find out whether it will cover your visit.

Before the Study

A sleep study requires some preparation, so it's smart to be aware of what's recommended before your test day.

Timing

Most sleep studies take place over the course of one night. A typical check-in time for a polysomnogram is between 8 and 10 p.m, The usual departure time after a person wakes up the next day is between 6 and 8 a.m. The goal is for the patient to sleep for at least seven hours, though this isn't always possible. If you work nights, some facilities can conduct studies during the day.

Rest Your Best

It may help to know that you may not need to sleep a full seven hours for a doctor to make a diagnosis.

Location

This test typically is done at a sleep center or sleep lab. This may be a special department that is part of a hospital or clinic. Or it may be a standalone facility. Sleep studies are sometimes even set up in hotels. Sleep labs may be accredited centers, which means they have met the standards of the American Academy of Sleep Medicine (AASM).

If your healthcare provider is ordering a sleep study for you, they will steer you in the direction of a lab that they are familiar with and trust. If you're seeking help on your own, be sure to research facilities in your area to find one that is accredited or has been reviewed favorably.

In general, a sleep center has multiple bedrooms that are set up for overnight sleep studies. These rooms are designed to be as comfortable and homey as possible, often with regular bedroom furniture (not clinical-looking hospital beds), a television, a private bathroom, and other amenities.

Typically, a sleep clinic is staffed with one or more healthcare providers who are trained in sleep medicine. Many also practice related disciplines, such as neurology, psychiatry, and pulmonary medicine. Other medical professionals typically found at sleep centers include physician assistants, nurses, respiratory therapists, and medical assistants.

Centers Exude Homeyness

For obvious reasons, sleep centers are designed to mimic the comforts of home.

How to Prepare

On the day of the study, you should follow your regular diet and daily routine as much as possible. Although you probably won't check in for your sleep study until evening, you'll need to keep a few things in mind during the day of the test:

  • Avoid caffeine in any form—coffee, tea, soft drinks, chocolate—after lunchtime.
  • Skip your evening cocktail or glass of wine. Alcohol in any amount can interfere with sleep.
  • Wash any hair gel or other styling products out of your hair. They can interfere with the sleep recording.
  • Do not nap during the day.
  • If you're on regular medication, make sure your healthcare provider knows what you take. You may need to stop taking it temporarily.

Recommended Sleep

The Centers for Disease Control and Prevention recommends that adults between the ages of 18 and 60 get at least seven hours of sleep per night. While the number is important, "good sleep quality is also essential."

What to Bring

It will be important to check with your sleep center to see if they have special restrictions for you. In general, though, you should bring the same items you would pack for an overnight stay at a hotel:

  • Medications that you take at night or in the morning that your healthcare provider has said you can continue during the test
  • Toiletries
  • Comfortable sleepwear and slippers or non-skid socks
  • Favorite pillows or blankets
  • A bedtime snack (there may be a small refrigerator in your room)
  • Phone charger
  • Book or other reading material (if it's part of your nighttime routine)
  • Something to eat for breakfast since the sleep center may provide coffee or juice but probably not food

If you have a spouse or partner, they will not be allowed to stay with you overnight. Parents of children undergoing a polysomnogram may be able to stay overnight in the sleep study room on a rollaway cot. A similar accommodation may be made for a patient with a condition such as dementia or a physical disability that makes it unsafe for them to be alone. Keep in mind that the room will be monitored throughout the night.

You won't be able to bring a pet, with the possible exception of a service animal. The animal will require proper documentation before it is granted entry.

Pack Light

It's a good idea to pack for an overnight stay at a sleep center as you would for an overnight stay at a hotel.

During Your Stay

You'll be asleep for most of the time you're being tested, but it's important to know what will happen so you can do your part to ensure that the results are as accurate and useful as possible.

Pre-Study

When you arrive for your sleep study, the process will be similar to checking in for any healthcare provider's appointment. There may be paperwork to fill out, including a consent form. And you may need to present your health insurance card and/or co-pay if you have one.

Once you're checked in, a sleep technician will take you to your bedroom for the night. They will show you the bathroom and where you can put your things. Then you'll have time to change into your sleepwear and go through your regular nighttime routine of brushing your teeth and washing your face. The technician will spend about 45 to 60 minutes setting you up for your sleep study. Some studies for seizures, for example, may take as long as 90 minutes to two hours to set up.

One of the tests that will take place while you sleep is an electroencephalogram (EEG), which measures electrical activity in the brain. To prepare you, the technician will measure the dimensions of your head and then use a special pencil to mark places on your scalp and face where the electrodes will be attached. (The marks wash off with soap and water.) They will then use a cotton swab to apply a mildly abrasive paste to each spot in order to remove the oil from your skin so that the electrodes will adhere properly.

The technician will apply a dab of a special paste that resembles cooking shortening to each disc and gently place it on the marked spots on your face and scalp. The paste keeps the electrodes in place and also allows them to better conduct the electrical waves from your brain. Some of the wires on your face may be taped in place. If you're sensitive to or allergic to medical tapes or glues, let the technician know ahead of time so that they can use a type that won't bother you.

Ask Questions

Be sure to ask your technician questions if you need clarification about any part of the sleep test. Technicians are trained to realize that the more a patient knows, the more likely they will be to relax.

In addition to the electrodes, several or all of the following may be part of your sleep study setup:

  • A flat, plastic microphone taped to your neck to record snoring
  • Sticky pads on your chest to monitor your heart rhythm via an electrocardiogram (EKG)
  • Stretchy cloth belts that go across the chest and stomach to measure breathing
  • Sticky pads or electrodes applied to the shins or forearms to monitor muscle movements via electromyography (EMG)
  • A peripheral capillary oxygen saturation monitor (usually clipped to a finger), measuring continuous oxygen saturation
  • An electro-oculogram (EOG), which uses electrodes placed near the eye to measure eye movements

All of these wires will be connected to a small, portable box that you can easily carry with you if you need to get out of bed (for a trip to the bathroom, for example). If you use a continuous positive airway pressure (CPAP) during the night, you may be fitted with a mask.

Finally, just before you go to bed, the technician will place a nasal cannula—plastic tubing that sits in the nose—that will measure airflow while you sleep. Most sleep clinics also use a thermistor, a pronged wire that sits in the nostrils and measures temperature changes

Once you're set up, the technician will leave you alone to read, watch television, or listen to music. It's important to not fall asleep until it's your usual bedtime or you feel drowsy enough to drift off. Let your technician know when this happens.

The technician will help you into bed and connect the wire box to a computer so that they can monitor you from another room. There will likely be a small infrared camera and two-way speaker in the room. If you need to get up during the night, this is how you will call for help to do that.

Just prior to going to sleep, the technician will test the equipment. As part of this testing, they will have you open and close your eyes, move them around, snore, take breaths in and out, and move your arms and legs. Still, if something goes wrong with a wire, or if one comes loose during the night, your technician will fix it.

Try Not to Fret

The wires involved in a sleep study can trip another type of wire: The wire of worry. But there is no need to fixate on them. They're long enough to let you move around and turn over in bed.

Sleep Aids

A common concern of people undergoing a sleep study is that they won't be able to sleep. Surprisingly, most people do sleep—despite the unfamiliar environment and all the wires. In fact, it's rare that someone isn't able to sleep at all.

If you're really worried about falling and staying asleep, your healthcare provider may have you take a medication that won't interfere with the various tests. The most common sleep aid is Ambien (zolpidem). Do not take this medication or any other without the approval of your healthcare provider.

In the worst-case scenario, the testing can be repeated to ensure that the results are valid.

Enjoy the Solitude

Cross off another concern from your list: You will have a sleep study room to yourself. You won't have to share it with anyone.

Throughout the Study

As you sleep, the electrodes and other equipment will monitor your brain waves, movements, sleep stages, and breathing patterns. The technician will keep a close eye on you from another room. If you wake during the night and need to get up for the bathroom or can't go back to sleep, you'll be able to contact the technician for help. Otherwise, you won't be aware of what's happening during the time you're asleep.

If sleep apnea is observed, treatment may be initiated with continuous positive airway pressure (CPAP) (if it's not in place already). It can help identify the pressure needed to improve your breathing.

Insomnia May Be Hereditary

If insomnia runs in your family, you may be dealing with it, too. Genetics plays a role in insomnia. Also, women are twice as likely to experience insomnia as men.


Post-Study

The technician will wake you at your regular wake-up time. They will remove your electrodes and other devices. And you may be asked to fill out a questionnaire about the quality of your night's sleep.

If your room has a shower and you're going to straight to work or an appointment, you can get ready there. You can also eat, drink, and take any of your regular medications.

Stress Can Rob Sleep


Stress can trigger a short-term sleep problem, or one that lasts from several days to several weeks. Chronic insomnia lasts longer and is often a symptom of another health condition, such as asthma, diabetes, or thyroid disease.

Interpreting the Results

You likely will not be given any information about your study until a sleep healthcare provider has had a chance to review the results. This probably will take some time. Sleep study reports can be as many as five pages long. They can be packed with hundreds of pieces of data about everything from the stages of sleep you went through and your breathing to your heart rate, oxygen levels, muscle movements, and snoring episodes.

The ASA lists the following specific aspects of sleep evaluation noted in most polysomnograms:

  • Sleep efficiency: These results quantify the total number of minutes you slept divided by the total amount of time you were recorded sleeping. The higher the sleep efficiency, the higher the percentage of sleep time versus awake time. Some reports also add up the amount of time a person is awake, as well as how much REM sleep and stage 1, 2, 3, and 4 sleep they get.
  • Apnea Hypopnea Index (AHI): This looks at how often a person experiences sleep apnea and hypopnea (partial obstruction). Five or more episodes usually leads to a diagnosis of sleep apnea.
  • Oxygen Desaturation Index (ODI): This refers to the number of times a person's oxygen level drops while they're asleep—useful information if someone is being assessed for sleep-disordered breathing. Oxygen levels above 90% are considered normal.
  • Heart rate: In general, a normal heart rate is between 60 and 100 beats per minute (BPM). If it exceeds this number, it's called tachycardia. Less than 60 BPM is known as bradycardia.

Your healthcare provider will review your study results with you and discuss possible treatments—at least if it turns out you have a sleep disorder.

AHI Explained

The AHI scale consists of two columns: The AHI and the sleep apnea rating. The AHI values and corresponding ratings are:


  • Less than 5 (<5): Normal, meaning no sleep apnea
  • 5 to 15: Mild sleep apnea
  • 15 to 30: Moderate sleep apnea
  • More than 30 (>30): Severe sleep apnea

Follow-Up

For those with excessive daytime sleepiness, multiple sleep latency testing (MSLT) may follow a diagnostic polysomnogram. This testing consists of opportunities to take naps at two-hour intervals the day following the overnight testing. It is somewhat simplified from the baseline study, with fewer measurements involved. The MSLT can identify narcolepsy, hypersomnia, or whether a normal amount of daytime sleepiness is present.

A maintenance of wakefulness test may also be performed as a follow-up. It's usually reserved for people who work in professions that require sustained alertness in order to preserve public safety. Truck drivers, airline pilots, train conductors, and other transportation professionals may be prime candidates for this test. Its goal is to ensure that in a quiet, somewhat darkened space, the patient can stay awake while slightly reclined. Transient dozing (or falling asleep) may be a problem if identified.

Repeat Sleep Studies

Sometimes it's necessary to repeat a sleep study. Your healthcare provider may suggest this course of action if you have:

  • Experienced changes in your health. A relatively modest change in weight—say, a loss or gain of 10% of your body weight—may justify a repeated sleep study, Sleep issues often improve with weight loss and worsen after weight gain. Abnormal sleep behaviors such as REM behavior disorder may develop later in life and should be assessed with a formal sleep study. Significant health changes could necessitate a second look, too. Heart failure, stroke, or the introduction of narcotic medications may all be reasons to ensure changes in breathing during sleep have not occurred.
  • Tried alternative treatments and your physician wants to measure their effectiveness. Some people turn to alternative therapies to treat sleep apnea, including the use of an oral appliance from a dentist or a surgical treatment. A second sleep study can be a useful way to check how the appliance works or whether the surgery was a success.
  • Unresolved sleep apnea. If you're still too sleepy, it may be a sign to dig a little deeper. Persistent and excessive daytime sleepiness may also require a reassessment of other conditions that may be triggering the fatigue. The Epworth Sleepiness Scale may be used again to gauge sleepiness. More intensive evaluation often proves necessary to sort out the underlying cause of the apnea.

Summary

Your healthcare provider may ask you to undergo a sleep study if you have trouble falling asleep, wake up frequently, snore, or have other symptoms of a sleep disorder. The study requires that you spend a night at a sleep center or sleep lab so that you can be hooked up to several types of monitors that literally track your every breath and movement. In the end, the report should give your primary care physician a good picture of your sleep quality (or lack thereof). To prepare for your visit, it's smart to pack as if you were going to a hotel but not actually staying at one (since you can't drink caffeine or alcohol before the study begins). Many people fear that they won't fall asleep (or stay asleep) during a sleep study. But the majority do.

A Word From Verywell

You may be wondering about taking matters into your own hands with an at-home sleep apnea test. Even the clinical director of the Johns Hopkins Sleep Medicine Program says the test offers advantages—namely, it's easy and cost-effective. But it's also limited. It's basically a breathing monitor that tracks breathing and oxygen levels. It's far less comprehensive than an overnight sleep study (and also features much different equipment). "A sleep test is meant to evaluate a patient for sleep apnea, and it monitors breathing parameters, not the sleep itself,” Susheel Patil says. Despite its limitations, you may decide that a home sleep apnea test suits your needs and interests. If so, ask your healthcare provider for a prescription. You'll need one since the test is not available over the counter. Your provider may beat you to the punch, though, by recommending an at-home test before you undergo a sleep study.

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6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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