A sleep study is a medical test that records your body's activity while you sleep. It is used to diagnose sleep apnea, restless leg syndrome, narcolepsy, REM behavior disorder, and other sleep disorders. There are two main types: in-lab polysomnography (PSG) and home sleep apnea testing (HSAT).
**When you need a sleep study.** Common reasons include loud chronic snoring, witnessed breathing pauses, excessive daytime sleepiness despite adequate time in bed, morning headaches, resistant high blood pressure, or an inability to stay awake during normal activities. A primary care doctor or sleep specialist orders the test.
**In-lab polysomnography: what happens.** You arrive in the evening with comfortable sleep clothes and toiletries. A technician places small sensors on your scalp, face, chest, and legs, plus a sensor on your finger to measure oxygen. Belts around your chest and abdomen track breathing effort. None of this is painful. You sleep in a private room that looks like a hotel room, and the technician monitors from another room.
**What the sensors measure.** EEG brain waves show sleep stages. EOG tracks eye movements for REM. EMG records chin and leg muscle activity. ECG monitors heart rhythm. Nasal airflow and respiratory effort sensors detect apneas and hypopneas. A pulse oximeter measures blood oxygen. A microphone or video may record snoring and body position.
**Home sleep apnea testing.** HSAT is a simplified version you do at home. You pick up or receive a small device, follow the instructions, and sleep in your own bed. It typically measures airflow, breathing effort, and blood oxygen. It is cheaper and more convenient, but it cannot diagnose disorders other than sleep apnea and may miss mild cases.
**During the night.** If a sensor comes loose, the technician may enter the room to reattach it. For suspected narcolepsy or REM behavior disorder, a daytime multiple sleep latency test (MSLT) may follow the overnight study. The MSLT measures how quickly you fall asleep during five scheduled naps.
**After the study.** A sleep specialist reviews the data and calculates an apnea-hypopnea index (AHI), which counts the number of breathing pauses or shallow breaths per hour. An AHI of 5–15 is mild, 15–30 is moderate, and over 30 is severe. Your doctor then explains the results and discusses treatment options.
**Getting your results.** Results usually take a few days to two weeks. Ask for a copy of the report and the AHI. If sleep apnea is diagnosed, treatment options include CPAP, oral appliances, positional therapy, weight loss, or surgery depending on severity and cause.