Types of Sleep Studies

Joseph Krainin, M.D.

Understanding the Different Types of Sleep Studies

types of sleep studies

Multiple types of sleep studies have been approved by the FDA. Due to the technical language, the options can be confusing. Each sleep study test type has unique features, benefits, and drawbacks. This article will break down the four different types of sleep studies and point you to the sleep study type that best meets your specific sleep testing needs.

Type 1 Sleep Study

Type 1 sleep studies are also known as in-lab sleep studies, polysomnography, polysomnograms, and [less commonly] polygraphs. Type 1 sleep studies are performed in an independent diagnostic and testing facility (IDTF or "sleep lab") or a sleep center. The difference between a sleep lab and a sleep center is that a sleep lab just does tests while a sleep center also has providers on site to diagnose and treat patients with sleep disorders. 

Type 1 sleep studies involve numerous electrodes applied to the body. An abrasive paste is used to scrub the skin to get a better connection and then the following sensors are attached: 

  • at least 6 EEG sensors that detect the patients’ brain electrical activity (brain waves)
  • 2 EOG sensors that record eye movement by detecting a voltage differences between the cornea and retina eye movements 
  • a single chin and two leg EMG sensors that measure the patient's muscle response or electrical activity in response to a nerve’s stimulation of the muscle
  • at least 2 ECG (EKG) leads which measure electrical activity from the heart and determine it's rhythm and rate

In addition, other sensors are applied that do not require scrubbing:

  • a nasal pressure transducer and a thermistor are placed under your nose to measure airflow
  • a pulse oximeter is placed on a finger to measure oxygen levels
  • two RIP belts are used to quantitatively measure breathing effort
  • a body position sensor

    A type 1 sleep study is attended by a sleep technologist and video will be obtained of the entire procedure through an infrared camera placed in the sleep study room. The CPT code for a diagnostic type 1 sleep study is 95810.

    Type1 sleep studies are considered the "gold standard" for diagnosing sleep disorders but home sleep apnea tests (HSATs or HSTs) are increasingly being used for the assessment of sleep apnea due to the following type 1 sleep study downsides:

    • high cost
    • often long wait times 
    • potential risk of exposure to infection
    • poor sleep efficiency and "the first night effect" which may lead to a misrepresentation of the sleep breathing disorder

    Type 1 sleep studies are still considered the mainstay for diagnosis of periodic limb movement disorder and as a part of the diagnostic evaluation for type 2 narcolepsy. They may be useful in the evaluation of parasomnias and nocturnal seizures. All of the above are rarely used reasons to refer someone for a sleep study. 

    At-Home Sleep Apnea Testing

    Home sleep apnea tests do not have the drawbacks of type 1 sleep studies but do have other limitations: 

    • no technical troubleshooting in real time if a sensor becomes loose or unattached
    • HSAT devices often don't accurately determine wake vs. sleep

    Type 2 Sleep Studies

    A type 2 sleep study is completed using a type II portable monitor and is not attended by a sleep technologist. A minimum of seven channels are recorded, including: electroencephalogram (EEG), electrooculography (EOG) , electromyography (EMG), electrocardiogram (ECG or EKG) or heart rate, airflow, respiratory effort and oxygen saturation.

    The type 2 sleep study diagnostic codes are: 

    • CPT code 95800 
    • G code G0398

    Type 2 Sleep Study Benefits: 

    • EEG allows for a very accurate determination of the AHI
    • EEG also potentially allows for the scoring of respiratory effort-related arousals (RERAs) which may give a better overall determination of the degree of sleep disordered breathing. Excessive RERAs have been associated with a condition called upper airway resistance syndrome
    • less expensive and more convenient than in-lab sleep studies
    • meets FAA requirements for pilots who need sleep apnea testing

    Type 2 Sleep Study Drawbacks:

    • the EEG may be difficult for patients to put on properly by themselves
    • these studies are more costly than types 2 and 3 sleep studies

    Type 2 Sleep Study Examples: 

    General Sleep Zmachine: The Zmachine Synergy is a high-tech in-home sleep monitoring system. With the Zmachine Synergy’s  EEG-based sleep staging and a 3D body position sensor, the AHI is calculated for both total sleep time and REM time. According to General Sleep, these calculations result in informative and accurate AHI values. The EEG also makes possible the reporting of RERAs (i.e. non-desaturating hypopneas terminating with EEG arousals) for improved event reporting.

    Philips Alice PDx: The Phillips Alice PDx is a sleep diagnostic recording device that is portable and intended for obstructive sleep apnea testing. This test incorporates Phillips’ unique Good Study Indicator (GSI). The GSI is predicated on airflow and oximeter signal quality and displays the amount of ‘good quality data’ needed for a study to be complete and valid.

    Type 3 Sleep Studies

    Type 3 sleep studies also does not need to be attended by a technologist and are completed using a type III portable monitor. A home sleep study type 3 records a minimum of four channels of information. This includes two respiratory movement/airflow channels, one ECG/heart rate channel and one oxygen saturation channel.

    Type 3 sleep study diagnostic codes: 

    • CPT code 95806
    • G code G0399

    Type 3 Sleep Study Benefits: 

    • the most commonly used home sleep study type; most sleep doctors are very familiar with interpreting the data from these devices
    • relatively cost effective compared to in-lab and type 2 sleep studies

    Type 3 Sleep Study Drawbacks: 

    • EEG is not measured so the REI (respiratory event index) is calculated on the assumption that the test taker was sleeping during the entirety of the recording

    Type 3 Sleep Study Examples: 

    Phillips Respironics Alice NightOne

    The Alice NightOne HST device was developed as a single-night sleep testing solution. A “smart guide” sequence guides patients through the setup process. The device provides feedback to the patient throughout the night. This device has three sensors (effort belt, cannula and oximeter). There is a built-in body position sensor as well, which provides a total of seven channels of data - body position, pressure flow, snoring, respiratory effort, SpO2, plethysmography and pulse rate.

      ResMed ApneaLink

      ResMed’s ApneaLink Air is a home sleep device that is lightweight, compact and simple to use. The ApneaLink Air is able to record up to five channels of information: respiratory effort, pulse, oxygen saturation, nasal flow and snoring.

      Type 4 Sleep Studies

      Type 4 sleep studies are also home-based sleep studies. Like types 2 and 3 sleep studies, they are not attended by a technologist. Type 4 sleep studies use peripheral arterial tonometry, which is a technology that measures changes in the finger artery, to accurately estimate abnormal breathing events. 

      Type 4 Sleep Study Diagnostic Codes:

      • CPT code 95800
      • G code G0400

       Type 4 Sleep Study Benefits: 

      • inexpensive
      • some options are disposable which can prevents infection from improperly cleaned types 2 and 3 sleep study devices
      • minimal sensors to apply; very user friendly

      Type 4 Sleep Study Drawbacks: 

      • the sleep doctor cannot read the raw data; the studies generate a report based on their systems' proprietary analysis of the PAT data and the doctor can only review the autogenerated numbers and sign the report
      • not as good at distinguishing obstructive from central sleep apnea as types 2 and 3 sleep studies

      Type 4 Sleep Study Examples: 


      The NightOwl home sleep apnea test is a small, 1-ounce sleep testing device that can test and record for up to 12 nights. The test is designed to be paired with a cellphone, then the device is placed on the finger with the sensor light touching the skin. Once an adhesive is wrapped around the patient’s finger to secure the device, recording can begin. Patients can upload their results to be reviewed by a physician within minutes. Total sleep time and REM sleep time are estimated based on actigraphy, which is like body movement tracking.


      WatchPAT provides AHI, AHIc, RDI and ODI based upon estimated sleep time and sleep staging. Some options include a snore sensor and a chest motion sensor that helps to differentiate obstructive from central respiratory events. After one minute of the test being complete, the patient’s raw data is downloaded and auto-scored 

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