What Is An Overnight Sleep Study (Polysomnogram)?

What to expect when undergoing this test

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A sleep study, more 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.

Since it can be strange to sleep somewhere other than your own bed and to know that you're being monitored and observed, you may feel some anxiety about the experience. The more you understand about why the test is important and what to expect, the more comfortable you'll feel.

sleep study setup
Illustration by Emily Roberts, Verywell

Purpose of Test

Your doctor may want you to have 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) known as the Epworth Sleepiness Scale.

Sleep studies are designed to diagnose sleep disorders, including:

Because self-reports don't paint a reliable picture about one's sleep, the test is necessary to get 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. The data collected from a full night's sleep is then interpreted.

Before the Test

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

Timing

Most sleep studies take place over the course of one night. According to the National Sleep Foundation, a typical check-in time for a polysomnogram is between 8 p.m. and 10 p.m, and the usual departure time after a person wakes up is between 6 a.m. and 8 a.m. The goal is for the patient to sleep for at least seven hours. If you work nights, some facilities are able to accommodate studies done during the day.

Location

This test typically is done at a sleep center or sleep lab. This may be a special department that's incorporated into a hospital or clinic, or it may be a stand-alone 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 doctor is ordering a sleep study for you, he will steer you in the direction of a lab that he's familiar with and trusts. If you're seeking help on your own volition, be sure to research facilities in your area to find one that is accredited or has been favorably reviewed.

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

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

Besides polysomnograms, most sleep centers also do other diagnostic tests for sleep disorders, as well as provide treatment.

How to Prepare

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

  • Steer clear of caffeine in any form—coffee, tea, soft drinks, chocolate—from lunchtime on the day of testing.
  • Skip your evening cocktail or glass of wine. Alcohol in any amount can interfere with sleep (even if you aren't aware of it).
  • Wash 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 doctor knows what you take. You may need to stop taking it temporarily.

Cost and Health Insurance

Sleep testing centers may be associated with a university or operate for-profit, with vastly different expenses charged for testing.

Overnight polysomnograms may cost from $600 to $5,000 (or more) for each night; the average is typically around $1000 to $2000 per night. Insurance, including Medicare, may cover the majority of this expense. Your ultimate costs will likely depend on your insurance type as well as specifics related to your annual deductible and other factors outlined in your policy.

According to the American Sleep Association (ASA), the criteria you must meet to have a sleep study covered by your insurance also varies. Most companies mandate that you be evaluated by a doctor and have certain symptoms before going to be tested. The organization cites the following symptoms as classic examples: excessive daytime sleepiness (EDS), snoring, witnessed apneas during sleep, nighttime gasping or choking, or change in certain behaviors.

Unfortunately, there are some policies that offer little or no coverage for the testing.
If you don't have insurance and plan to pay out of pocket for your sleep study, the center may charge you less than it would typically charge an insurance company.

If you are concerned about the costs of your sleep evaluation, it is best to call ahead and get the information from the testing center or your insurance company prior to having the study. (The specific billing codes can be disclosed by your medical provider.) Any reputable sleep center, especially those associated with healthcare centers, should be able to provide you with an estimate of the expense prior to your evaluation. This is the best way to avoid any costly surprises.

Alternatively, if you're being evaluated for sleep apnea, as your doctor about a home sleep apnea testing. This option, which involves borrowing equipment from a provider and setting it up and using it on your own, is significantly less expensive. In general, these tests may cost closer to $200 to $600 per night and are often covered by most insurance companies, according to the ASA.

Note: At-home test devices do not record sleep stages, heart rhythms with EKG, or leg movements. They focus on measuring breathing patterns, air flow, and oxygen levels. They also record pulse rates and sleep position. Home sleep apnea testing is best for identifying moderate to severe cases. If the test is inconclusive, an in-center test may be required.

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 usually pack for an overnight stay at a hotel:

  • Medications that you take at night or in the morning that your doctor has said you can continue during the test
  • Toiletries
  • Comfortable sleepwear and slippers or non-skid socks (If you don't routinely wear clothing to bed, you'll need to do so for the sleep study.)
  • Favorite pillows or blankets
  • "Comfort items" needed to sleep
  • A bedtime snack (there may be a small refrigerator in your room)
  • Phone charger
  • Book or other reading material, if part of your nighttime routine
  • Something to eat for breakfast. The facility may provide coffee or juice, but don't expect anything else.​

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. You'll need to clear bringing the pet ahead of time and supply any required documentation.

During the Test

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-Test

When you arrive for your sleep test, the process will be similar to checking in for any doctor'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. She will show you the bathroom and where you can put your things, and then leave you to start settling in, change into your sleepwear, and go through your regular nighttime routine of brushing your teeth, washing your face, and so forth.

The technician will then spend about 45 to 60 minutes setting you up for your sleep study. This time can vary, depending on their efficiency and the complexity of your individual set-up. 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 will wash off with soap and water.) She'll then use a cotton swab to apply a mildly abrasive paste to each spot in order to remove the oils 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 she can use a type that won't affect you.

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 electromyography (EMG)

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. Enjoy the time to yourself—read, watch television, 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 that happens. (She will have instructed you as to how to contact her.)

The technician will then help you into bed and connect the wire box to a computer so that she can monitor you from another room. There will likely be a small infrared camera and two-way speaker in the bedroom. 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 need to test the equipment. As part of this testing, she'll have you open and close your eyes, move them around, snore, take breaths in and out, and even move your arms and legs. If something goes wrong with a wire, or if one comes loose during the night, your technician will come in to fix it.

Sleep Aids

A common concern of people undergoing a sleep study is that they won't be able to sleep. Surprisingly, most individuals are able to sleep, even with all the wires, the strange environment, and any number of things that could be disruptive. It is exceptionally rare that someone isn't able to sleep at all.

If you're really worried about this, your doctor 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 OK from your doctor.

In the worst-case scenario, the testing can be repeated as necessary to ensure adequate sleep observation is obtained and the results are valid.

Throughout the Test

As you sleep, the electrodes and other equipment will be monitoring your brain waves, movements, sleep stages, breathing patterns, and so on. The technician will be keeping a close watch 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 not in place already) to find the appropriate pressure to improve your breathing.

Post-Test

The technician will wake you at your regular wake-up time. She'll remove your electrodes and other devices quickly—within 10 minutes or so. There may be a questionnaire about your night's sleep to complete.

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.

Interpreting Results

You likely will not be given any information about your study until a sleep doctor 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 and packed with hundreds of pieces of data about everything from the stages of sleep you went through and your breathing, heart rate, oxygen levels, muscle movements, episodes of snoring, and more.

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

  • Sleep efficiency: These results quantify the total number of minutes a person sleeps during a sleep study divided by the total amount of time they 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 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). More than five episodes of either is considered an abnormal AHI in adults and 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 percent are considered normal.
  • Heart rate: In general, a normal heart rate is between 60 and 100 beats per minute (BPM). If it goes over this number it's called tachycardia. Less than 60 BPM is regarded as bradycardia.

    You'll make an appointment to meet with the doctor to review these findings and others from your study and discuss possible treatments, if it turns out you have a sleep disorder.

    Follow-Up

    For those with excessive daytime sleepiness, multiple sleep latency testing (MSLT) may follow a diagnostic polysomnogram. It 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—for example, truck drivers, airline pilots, train conductors, or other transportation professionals. This test ensures that, in a quiet, somewhat darkened space, the tested individual can stay awake while slightly reclined. Transient dozing (or falling asleep) may be a problem if it is identified.

    Repeat Sleep Studies

    Sometimes it's necessary to do a sleep study over.

    Changes in your health: If a sleep study was performed some years ago, there may be significant changes in your health that necessitate a reassessment of your sleep. A relatively modest change in weight, either gaining or losing 10 percent of your body weight, may be a reason to repeat a study. Weight gain will often worsen the degree of sleep apnea while losing it might improve or even fully alleviate the condition.

    Symptoms that you have developed that were not present at the time of your initial diagnosis may also prompt a repeat sleep assessment. For example, if you newly have restless legs syndrome or are noted to have frequent leg movements at night, this may require evaluation. In addition, abnormal sleep behaviors such as REM behavior disorder may develop later in life and should be assessed with a formal sleep study.

    Finally, even more significant health changes could necessitate a second look. Heart failure, stroke, or the introduction of narcotic medications may all be reasons to ensure changes in breathing during sleep have not occurred. Each of these conditions can be associated with central sleep apnea, a disorder that often requires bi-level therapy.

    Assessment of the success of alternative treatments: Many people choose alternative therapies to treat sleep apnea, including the use of an oral appliance from a dentist or surgical treatments. A second sleep study can be a useful way to check on how your appliance works or whether the surgery was a success.

    The oral appliance can be worn while a standard sleep study is performed to evaluate your breathing. A study can also be done postoperatively, typically two months or longer after the surgery was performed. It is important to compare apples to apples and orange to oranges: have the same type of study (and at the same location) as your prior testing to ensure that other variables do not undermine the comparisons. If sleep apnea persists despite these treatments, it is often necessary to reconsider other therapy options.

    Unresolved symptoms and optimizing CPAP therapy: Sometimes a sleep study is repeated to address unresolved symptoms. If you are still too sleepy, this may be an indication to dig a little deeper. These repeat studies also allow for optimization of treatments, including the titration of CPAP therapy.

    Persistent excessive daytime sleepiness may require reassessment as other conditions may be occurring. 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 state. It may occur due to sleep deprivation, undertreated sleep apnea, narcolepsy, or other factors. A diagnostic polysomnogram followed by multiple sleep latency testing (MSLT) may provide evidence as to the cause.

    The most common indication for the second night of sleep study is to initiate and optimize positive airway pressure treatment to remedy sleep apnea. It sometimes proves impossible to find the most effective pressure settings either as part of an initial split night study or with a trial of therapy at home. Instead, a second titration study can be used to ensure proper mask fitting, improve acclimatization to the therapy, and identify the necessary pressures to maintain the airway during sleep. In some cases, alternative therapies can be explored including CPAP, bilevel, and even auto or adaptive servo-ventilation (ASV). The sleep technician can work with you to optimize the therapy experience.

    A Word From Verywell

    As a diagnostic test, a sleep study definitely is one of the more time-consuming evaluations. It also may be one of the strangest, given it requires wearing all sorts of electrodes, wires, and other monitoring devices and being watched while you sleep. Sleep centers do all they can to make patients feel right at home, though. This should be your experience as well, but you'll need to prepare for the test properly: This is the best way to get the results necessary to diagnose your sleep disorder (if you have one) and get you on the road to finally getting a good night's rest.

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    Article Sources
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    • American Academy of Sleep Medicine. Clinic vs. Lab Fact Sheet. https://aasm.org/clinic-versus-lab-fact-sheet/
    • National Sleep Foundation. What Happens During a Sleep Study. https://sleep.org/articles/what-happens-during-sleep-study/
    • Harvard Medical School. Narcolepsy: Epworth Sleepiness Scale. Feb 21, 2018. http://healthysleep.med.harvard.edu/narcolepsy/diagnosing-narcolepsy/epworth-sleepiness-scale
    • American Sleep Association. Sleep Study Results. https://www.sleepassociation.org/sleep-disorders/sleep-apnea/interpret-sleep-study-results/