What happens at a sleep study? An in-lab sleep test, step by step

At an in-lab sleep study, you spend one night at a sleep center while painless sensors record your brain waves, breathing, heart, oxygen and movements. A technologist watches from a nearby room, and a sleep doctor reviews the recording afterward. It's the most complete way to check for sleep apnea, and most of the night is simply going to sleep with some wires on.

What is a sleep study?

A sleep study is an overnight test, formally called polysomnography, that records how your body works while you sleep. The American Academy of Sleep Medicine (AASM) says it records brain waves, heart rate and breathing, and also tracks eye, leg and arm movements and the oxygen level in your blood.

Doctors use it to test for sleep-related breathing disorders such as sleep apnea, to look into unusual behaviors during sleep, as part of checking for narcolepsy, to set the right air pressure for CPAP, and to find out why a sleep treatment isn't working. Cleveland Clinic says it can help diagnose both obstructive and central sleep apnea, periodic limb movements and some seizure disorders, among others.

Sleep studies are common. Cleveland Clinic notes that people on Medicare alone accounted for more than 800,000 sleep studies in 2014.

How do you get diagnosed with sleep apnea?

Getting diagnosed with sleep apnea starts with your own doctor, who asks about your sleep and symptoms and then orders a test. A sleep doctor reads the results and makes the diagnosis. The AASM recommends against diagnosing sleep apnea from questionnaires or prediction tools alone, without a sleep study or home test.

The usual path looks like this:

1. You or a bed partner notice signs such as loud snoring, gasping, pauses in breathing or daytime sleepiness. Our list of sleep apnea warning signs covers what to watch for.
2. You talk to your doctor. Our list of questions to ask your doctor about snoring can help you prepare.
3. Your doctor orders either a home sleep apnea test or an in-lab sleep study.
4. A sleep doctor interprets the test, and you go over the results and treatment options together.

The AASM's 2017 diagnostic guideline says either polysomnography or a home sleep apnea test with an adequate device can be used for uncomplicated adults with signs of moderate to severe obstructive sleep apnea. It recommends in-lab polysomnography instead of a home test for people with significant heart or lung disease, possible breathing-muscle weakness from a neuromuscular condition, a history of stroke, long-term opioid use or severe insomnia.

How do you prepare for a sleep study?

Preparing for a sleep study is mostly about keeping your day normal and arriving with clean skin and hair. The AASM suggests following your usual routine, avoiding naps and avoiding caffeine after lunch. It also says to skip hair sprays and gels, which can interfere with the recording, and to avoid alcohol and sedatives unless your doctor prescribed them.

Cleveland Clinic's advice is a little stricter on timing. It suggests avoiding caffeine and alcohol for at least eight hours before the study, and showering beforehand but skipping creams, lotions and hair products afterward so the sensors stick. Nail polish and fake nails can affect the fingertip oxygen sensor. Your lab's own instructions come first.

On medicines, take them as usual unless your provider tells you otherwise. Cleveland Clinic warns that stopping some medicines suddenly can have unpleasant or dangerous effects. Tell the team about any skin allergies, since the adhesives can irritate some people.

Pack as if you're staying in a hotel for one night: comfortable pajamas, a toothbrush and toothpaste, makeup remover, something to read and clean clothes for the morning.

What happens when you arrive?

You usually arrive in the early evening, the AASM says. A sleep technologist asks about your sleep habits, and you may fill out a questionnaire. You'll have the room to yourself, with a bathroom and sometimes a TV. People who work nights can often book a daytime study, according to Cleveland Clinic.

What sensors do they put on you?

The technologist attaches sensors with glue, gel or tape. The AASM says they're painless. Each one tracks a different part of your sleep, which is what makes an in-lab study more complete than a home test.

Sources: Cleveland Clinic and the AASM.

Once everything is on, you'll be asked to move your eyes, clench your teeth or open and close your mouth, and move your legs so the team can check each sensor is working.

What happens during the night?

During the night, you go to sleep as normally as you can while the equipment records. The AASM says you're free to read or watch TV until your usual bedtime. When the lights go off, a low-light video camera lets the technologist see you from a nearby room.

The wires are long enough for you to turn over and sleep on your side. If a sensor comes loose, staff will come in and reattach it. If you need the bathroom, they'll help with the wires. Cleveland Clinic advises not unplugging anything yourself unless staff have shown you how.

Many people worry they won't sleep. The AASM says most patients don't sleep as well as at home, which usually doesn't affect the results, and that nearly everyone falls asleep. You don't need a full eight hours. Cleveland Clinic says a study is generally considered valid if you sleep a total of two hours or more. Occasionally a doctor prescribes medicine to help you sleep during the study.

Cleveland Clinic also says staff won't watch you the whole time. The cameras are mainly there to check unusual readings and match the video to the sensor data.

What is a split-night sleep study?

A split-night sleep study combines diagnosis and treatment in one night. The first part records your sleep to diagnose sleep apnea, and if it's clear and severe enough, the technologist fits a CPAP mask and adjusts the pressure in the second half. The AASM says this is usually only offered when sleep apnea is severe and the diagnosis is clear.

The AASM's 2017 guideline sets two conditions. Moderate to severe sleep apnea must be seen during at least 2 hours of recording, and at least 3 hours must be left to complete the CPAP adjustment. If either isn't met, the whole night is used for diagnosis.

When CPAP is set on a separate night, it's called a CPAP titration study. You're fitted with a nasal or full-face mask, and the technologist changes the pressure remotely through the night. The AASM says pressure starts very low and gradually increases, and you should tell the technologist if the mask is uncomfortable or leaks. The AASM's 2019 treatment guideline says CPAP can be started either with an in-lab titration or with an auto-adjusting machine at home in adults with no significant other conditions.

What happens in the morning?

In the morning, the technologist checks the sensors and removes them, and you may fill out a short questionnaire about how you slept. The AASM says the study is complete once you're awake and the sensors are off. You can leave and go about your day. Cleveland Clinic says the main side effects are skin irritation from the adhesives and a less restful night than usual.

How do you get your sleep study results?

Sleep study results come from your doctor after the sleep team has reviewed the recording. The AASM says a technologist first scores the study, marking sleep stages and any abnormal breathing or leg movements, and then a sleep doctor reviews it and makes the diagnosis. This can take up to two weeks. Cleveland Clinic says a provider usually reaches out within a few days, and that it varies by facility.

For sleep apnea, the report includes your apnea-hypopnea index, or AHI, which counts breathing pauses and shallow breaths per hour. Our guide to what AHI means explains the numbers. The report also shows whether the events were obstructive or central. The AASM says central sleep apnea is identified on polysomnography, and some people are asked back for a second night with CPAP. Our article on central sleep apnea explains that type.

If you're diagnosed, your doctor will talk through treatment. The AASM calls CPAP the leading treatment for sleep apnea, and our guides to getting used to CPAP and sleep apnea treatment options cover what comes next.

How is an in-lab study different from a home sleep apnea test?

An in-lab study records more than a home test does. Cleveland Clinic says home tests usually skip the sensors for brain waves, eye movements and heart rhythm, and focus on airflow through the nose or mouth and breathing movement in the chest and belly. They're mostly used when sleep apnea is strongly suspected, or for follow-up after treatment such as surgery or weight loss.

Because a home test doesn't record brain waves, it can't tell when you're actually asleep, and a negative result doesn't rule sleep apnea out. The AASM recommends an in-lab sleep study if a single home test is negative, inconclusive or technically inadequate, rather than repeating the home test. Our guide to the home sleep apnea test explains who it suits and what the kit looks like.

Either way, the test is the important step. If you snore loudly, gasp at night or feel sleepy during the day, ask your doctor which test is right for you. Our article on snoring vs sleep apnea can help you describe what's been happening.

This article is general information, not medical advice.

Read next

• What is a home sleep apnea test, and what should you expect?
• What is AHI? The apnea-hypopnea index and what your number means
• Getting used to CPAP: your first weeks

* This content is for informational and educational purposes only and is not medical advice. It is not intended to diagnose, treat, cure or prevent any disease or health condition. Talk to a qualified healthcare provider about your health.