Sleep study, also called polysomnography (PSG) is a multi-parametric test that is used to study sleep. It is also used as a diagnostic tool in sleep medicine. The result of the test is called polysomnogram derived from Greek and Latin words.

Sleep study is an in depth recording of the biophysical changes during sleep. During the period of sleep, body functions are monitored. This includes the brain, eye movements, muscle activity and heart rhythm. In the discovery of sleep apnea in 1970's, monitoring of other physiological functions is necessary which includes breathing functions respiratory airflow and respiratory effort along with the use of peripheral pulse oximeter.

The test is specifically used in ruling out several types of disorders including narcolepsy REM behavior disorder, parasomnias and sleep apnea. It is frequently ordered by doctor for patient with daytime fatigue. It records a minimum of twelve channels requiring a minimum of 22 wires attached to the patient. Three channels for the EEG, one or two measure airflow, one for chin muscle tone, another one for leg movements, two for eye movements, one for the heart rate and rhythm, one for oxygen saturation and the last one for each belts which measure wall movement. The data gathered from the wires that comes from the patient meets into a central box. It is connected to computer system for recording, storing and displaying of the obtained data. The computer monitor will now display multiple channels. Small video cameras are inputted for the technician to be able to observe the patient visibly from an adjacent room. Technicians observes sleep activity by looking at the video monitor and on the computer monitor which displays all the data time to time.

Sleep labs could have been done in different venues. It is perhaps done in the hospital, medical office or in hotels. It can also be done in homes as the physician may prescribe home studies enhancing patient comfort and also reducing the expense. Screening tools that are typically used by the patient includes a thermostat and pulse oximeter. In determining changes in blood oxygen levels occurring with sleep apnea and other respiratory problems, a pulse oximeter is recommended to use.

After the completion of the test, the clinician analyzes the data by studying it for only 30 second time period. The test recording and the screening data are always sent to the sleep physician physician for interpretation. The clinician then writes a report with recommendations based on the test results.