Sleep Studies Explained: Home Test vs In-Lab Polysomnography

Why sleep studies are done

Sleep studies help diagnose conditions such as obstructive sleep apnea, central sleep apnea, narcolepsy, periodic limb movements and some parasomnias like REM sleep behavior disorder. Insomnia is usually diagnosed from your history and a sleep diary rather than a study, unless another disorder is suspected.

Home sleep apnea test (HSAT)

A home sleep apnea test uses a small portable device you wear in your own bed, usually for one to three nights. Sensors typically include a nasal cannula to measure airflow, belts around the chest and abdomen to measure breathing effort, and a finger clip (oximeter) to measure oxygen levels and pulse.

According to the AASM's 2017 clinical practice guideline, a home test is appropriate for adults with signs and symptoms suggesting moderate to severe obstructive sleep apnea who do not have significant heart, lung or neuromuscular conditions or other suspected sleep disorders. It is convenient and less costly. Because most home tests do not measure brain waves, they cannot tell exactly when you are asleep and may underestimate sleep apnea. If a home test is negative or inconclusive but symptoms suggest sleep apnea, an in-lab study is recommended.

In-lab polysomnography (PSG)

An in-lab study is done overnight at an accredited sleep center, in a private room that usually resembles a simple hotel room. A technologist attaches sensors that record:

• Brain waves (EEG), eye movements (EOG) and chin muscle tone (EMG) to identify sleep stages
• Heart rhythm (ECG)
• Airflow, breathing effort and blood oxygen
• Leg movements, snoring and body position
• Often video and audio

It is the most complete test and is used for people with complex medical conditions, suspected disorders other than sleep apnea, or inconclusive home tests.

Split-night and titration studies

If significant sleep apnea is found in the first part of a lab night, the technologist may start CPAP for the rest of the night to find the right pressure. This is called a split-night study. A separate full-night titration study may be done instead. If you will be using an auto-adjusting CPAP, a titration study may not be needed.

Daytime tests for sleepiness

The Multiple Sleep Latency Test (MSLT) measures how quickly you fall asleep during a series of daytime nap opportunities and is used to help diagnose narcolepsy and idiopathic hypersomnia. It is usually done the day after an overnight study. The Maintenance of Wakefulness Test measures your ability to stay awake, sometimes for safety-critical jobs.

How to prepare

• Follow your usual routine and avoid naps on the day of the study.
• Avoid caffeine in the afternoon and alcohol in the evening unless instructed otherwise.
• Wash your hair and skip oils or gels, which can interfere with sensors.
• Bring comfortable sleepwear, your pillow if you like, and your usual medicines; ask the center which medicines to take.
• Do not worry if you think you sleep badly. Most people sleep enough for a useful result.

Understanding your results

The key measure for sleep apnea is the apnea-hypopnea index (AHI) or, for many home tests, the respiratory event index (REI): the average number of breathing pauses or reductions per hour. For adults:

• Fewer than 5 per hour: normal
• 5 to 14: mild
• 15 to 29: moderate
• 30 or more: severe

Your report may also show lowest oxygen saturation, time spent below certain oxygen levels, sleep efficiency and leg movements. A sleep physician interprets the results together with your symptoms and health history and discusses treatment options, such as CPAP, oral appliances or other therapies.