Polysomnography, usually shortened to PSG, is the most detailed form of overnight sleep testing. Unlike a home sleep apnea test, which focuses mainly on breathing, a full polysomnogram records several body systems at the same time while you actually sleep. That allows specialists to see not only whether breathing is being disrupted, but what is happening to sleep itself.
A typical laboratory study records brain-wave activity using EEG, eye movements, muscle activity, heart rhythm, breathing effort, airflow and blood oxygen. Leg movements are usually monitored as well, and some laboratories add video. Because brain activity is recorded, the study can determine when you are awake, when you are asleep and how much time you spend in different sleep stages.
That extra information is the key difference from most home sleep apnea tests. A home test may be entirely appropriate when the main question is straightforward obstructive sleep apnea. But polysomnography can reveal whether breathing events are actually causing arousals, how they change across REM and non-REM sleep, whether oxygen levels fall, whether unusual movements are occurring and whether another sleep disorder may be contributing to the problem.
In the United States, the American Academy of Sleep Medicine considers polysomnography the standard diagnostic test when obstructive sleep apnea is suspected following a comprehensive sleep evaluation. For otherwise uncomplicated adults at increased risk of moderate to severe OSA, either PSG or an appropriate home sleep apnea test may be used. But if a home test is negative, inconclusive or technically inadequate while suspicion remains, the AASM recommends polysomnography.
There are also situations where going directly to laboratory testing can make more sense. AASM guidance recommends PSG rather than home apnea testing when suspected sleep apnea occurs alongside significant heart or lung disease, possible respiratory muscle weakness, suspected sleep-related hypoventilation, chronic opioid use, a previous stroke or severe insomnia.
PSG is not limited to obstructive sleep apnea. Depending on the clinical question, laboratory monitoring can help investigate central sleep apnea, periodic limb movements and certain unusual nighttime behaviors or suspected parasomnias. When narcolepsy or another disorder of excessive sleepiness is suspected, an overnight PSG may be followed the next day by a Multiple Sleep Latency Test, or MSLT.
Importantly, this does not mean everyone with insomnia needs a sleep study. Polysomnography is usually not required for straightforward chronic insomnia when there are no signs suggesting another sleep disorder. In the US, Medicare coverage policies specifically do not treat PSG as a routine diagnostic test for chronic insomnia alone. Its value is greatest when there is a reason to suspect that something measurable is happening during sleep that cannot be established from symptoms alone.
The experience is more involved than home testing but generally straightforward. You spend a night in a sleep center or hospital sleep laboratory with sensors attached to the scalp, face and body. A sleep technologist monitors the recording while you sleep. The equipment looks extensive, but the purpose is to capture enough physiological information to reconstruct what happened throughout the night.
Sometimes a US sleep center may perform a "split-night" study. If clear moderate to severe obstructive sleep apnea appears early enough in the night, the second part of the study can sometimes be used to determine an appropriate CPAP pressure rather than requiring a separate night. AASM guidance supports this approach when sufficient diagnostic recording time and enough time for CPAP titration remain.
Access in the US is commonly through a sleep medicine specialist, primary care clinician, pulmonologist, neurologist or accredited sleep center. Insurance requirements vary, and some insurers may require home testing first when uncomplicated obstructive sleep apnea is the main concern. Medicare also covers clinically indicated sleep testing under defined circumstances, so checking the specific plan and sleep facility before testing is sensible.
In the UK, the pathway is slightly different. If sleep apnea is suspected, NICE recommends home respiratory polygraphy as the initial investigation for most adults rather than automatically sending everyone for overnight polysomnography. PSG becomes particularly valuable when simpler home testing has not adequately explained the symptoms or when a more complex sleep disorder needs investigation.
NHS specialist sleep centers therefore use a stepped approach. Royal Papworth Hospital, for example, offers simple overnight oximetry and home respiratory polygraphy first for appropriate patients, while inpatient polysomnography is used when those tests are insufficient or more detailed investigation is required. Its PSG service records EEG and other physiological signals and can identify disruption from conditions including sleep apnea and limb movements.
A UK patient would normally reach an NHS sleep service through a GP or specialist referral. Private sleep clinics also offer overnight polysomnography, which may provide quicker access but can be substantially more expensive than a home study. Whichever route is used, the important issue is not simply obtaining more data. It is choosing the test that matches the question being investigated.
Polysomnography is therefore best thought of as a diagnostic investigation rather than a sleep-improvement technique. If someone simply takes a long time to fall asleep, PSG may add little. But if sleep remains unexplained despite reasonable interventions, or there are clues such as snoring, breathing pauses, abnormal movements, unusual nighttime behaviors, severe daytime sleepiness or an inconclusive home apnea test, seeing what the brain, breathing, oxygen levels and body are actually doing throughout the night can reveal something that a sleep diary cannot.
