What Is Polysomnography
Polysomnography is an overnight diagnostic test that records multiple physiological signals while you sleep. Electrodes and sensors placed on your scalp, face, chest, and legs capture brain wave activity, eye movements, muscle tone, heart rhythm, breathing patterns, and blood oxygen levels simultaneously. The test typically lasts 6 to 8 hours and produces a detailed record called a polysomnogram, which sleep specialists analyze to diagnose sleep disorders.
Unlike simple screening tools, polysomnography provides the gold standard data for detecting obstructive sleep apnea, central sleep apnea, narcolepsy, periodic limb movement disorder, and REM sleep behavior disorder. The test captures data across all sleep stages (N1, N2, N3, and REM), showing how your brain and body function during each phase.
What Gets Measured
- EEG (electroencephalogram): Records brain electrical activity to identify sleep stages and detect abnormal patterns
- EOG (electrooculogram): Tracks eye movements to confirm REM sleep and detect certain sleep disorders
- EMG (electromyogram): Measures muscle tone in the chin and legs to detect muscle atonia during REM sleep or leg movements
- Airflow sensors: Monitor breathing through the nose and mouth to identify apneas (breathing stops lasting 10 seconds or longer)
- Chest and abdominal effort bands: Show whether breathing attempts occur during apneas
- Pulse oximetry: Measures blood oxygen saturation (normal is above 95% during sleep)
- EKG: Records heart rhythm to detect arrhythmias triggered by oxygen drops
- Body position sensor: Tracks whether apneas worsen when you sleep on your back
When It's Ordered
Your doctor typically recommends polysomnography if you have symptoms suggesting sleep apnea (loud snoring, witnessed breathing pauses, excessive daytime sleepiness), suspected narcolepsy, unexplained insomnia that hasn't improved with cognitive behavioral therapy for insomnia, or periodic leg movements disrupting sleep. Insurance companies including Medicare usually require polysomnography before approving CPAP therapy for obstructive sleep apnea.
What to Expect During the Test
You arrive at a sleep lab 30 minutes before bedtime. A sleep technician attaches 15 to 20 electrodes using conductive paste and secures them with adhesive strips or elastic bands. Most people find this process uncomfortable but tolerable. You sleep in a private room monitored by video and audio, with a technician present to replace any loose sensors. You can call the technician if you need a bathroom break, and they'll temporarily disconnect the mobile leads. The full night's data is then reviewed by a board-certified sleep medicine physician within 3 to 7 days.
How Results Are Interpreted
Key measurements from your polysomnogram include your Apnea-Hypopnea Index (AHI), which counts breathing disruptions per hour of sleep. An AHI below 5 is normal, 5 to 15 is mild sleep apnea, 15 to 30 is moderate, and above 30 is severe. Your oxygen saturation nadir (lowest point reached) and arousal index (how many times per hour your sleep was disrupted) also guide diagnosis and treatment decisions. The report notes your sleep efficiency (percentage of time in bed actually spent asleep) and whether sleep-related breathing events cluster in certain sleep positions or stages.
Common Questions
- Will I sleep normally during polysomnography? Most people sleep adequately, though some experience the "first night effect" where they sleep less than usual. Even partial data is diagnostic. If sleep deprivation interferes with results, your doctor may recommend a second night or split study (one night for diagnosis, one for CPAP titration).
- Can I do polysomnography at home? Home sleep apnea tests (HSAT) are available for obstructive sleep apnea screening but are less comprehensive than lab studies. They measure airflow, breathing effort, and oxygen levels but not brain activity or sleep stages. Labs remain necessary for suspected narcolepsy, EEG abnormalities, or when home testing results are inconclusive.
- How much does it cost? Polysomnography typically costs $1,200 to $3,000 without insurance, though prices vary by region and facility. Most insurance plans cover it when medically necessary, often requiring prior authorization.