What are the different types of sleep studies, Type 1 to Type 4?

CMS sorts sleep tests for obstructive sleep apnea into four types. Type I is attended in-lab polysomnography. Type II uses at least 7 channels and monitors sleep staging. Type III uses at least 4 channels covering breathing, heart rate and oxygen saturation. Type IV covers devices that do not meet all the criteria of a higher category.¹

By Wesper. Published November 2, 2026.

How are sleep studies classified?

CMS classifies sleep testing for obstructive sleep apnea (OSA) by setting and by the channels a device records, in National Coverage Determination (NCD) 240.4.1, effective March 3, 2009.¹ You will also see the categories written as Type 1 to Type 4, or as Level 1 to Level 4. This article uses the Roman numerals that CMS uses, and the table summarizes the NCD definitions along with the settings named in its coverage language.¹

What is a Type I sleep study?

A Type I study is attended, facility-based polysomnography (PSG), which the NCD describes as the reference standard for diagnosing OSA.¹ It uses the full channel set shown in the table, recorded in a sleep laboratory facility where a technologist supervises the recording and can intervene if needed.¹

The AASM's patient page describes polysomnography as a study that records brain waves, heartbeats and breathing, and also tracks eye, leg and arm movements and blood oxygen levels.² A sleep technologist scores the study by marking sleep stages and identifying events of abnormal breathing or leg movement.² Because sleep is staged, PSG can report an apnea-hypopnea index (AHI), defined as apneas plus hypopneas times 60, divided by total sleep time.³

What are Type II and Type III sleep studies?

Type II and Type III studies are defined by minimum channel counts, and the NCD's coverage language allows both to be performed unattended in or out of a sleep lab facility or attended in one.¹ Type II requires a minimum of 7 channels, and the NCD notes that this type monitors sleep staging, so AHI can be calculated.¹

Type III requires a minimum of 4 monitored channels, including ventilation or airflow, heart rate or ECG, and oxygen saturation.¹ The ventilation or airflow requirement means at least two channels of respiratory movement, or respiratory movement plus airflow.¹ The Type III definition does not call for sleep staging.¹

What is a Type IV sleep study?

Type IV is the broadest category, covering devices that may measure one, two, three or more parameters but do not meet all the criteria of a higher category.¹ Some of these monitors use an actigraphy algorithm to identify periods of sleep and wakefulness.¹

The NCD covers Type IV devices when they measure three or more channels, one of which is airflow.¹ Separately, the NCD covers devices measuring three or more channels that include actigraphy, oximetry and peripheral arterial tone.¹ Because Type IV starts at a single parameter, coverage depends on which channels a specific device records.¹

How do these types map to the term "home sleep apnea test"?

Based on the AASM and CMS definitions, the term fits unattended Type III and Type IV studies most closely.^{1, 3} The AASM defines home sleep apnea testing as "the use of unattended diagnostic studies to assess for obstructive sleep apnea without the determination of sleep stage."³ Type I studies are attended and Type II devices monitor sleep staging, so neither matches that definition.¹

The CMS type does not by itself establish whether a device is technically adequate under the 2017 AASM clinical practice guideline. The guideline calls for, at a minimum, nasal pressure, chest and abdominal respiratory inductance plethysmography and oximetry, or else PAT with oximetry and actigraphy, plus at least 4 hours of technically adequate oximetry and flow data from a recording attempt that encompasses the habitual sleep period.⁴

Because HSAT does not determine sleep stage, results are reported as a respiratory event index (REI), calculated as the total number of respiratory events scored times 60, divided by monitoring time, and the AASM style guide says REI should be used for home sleep apnea testing.³ Our article on REI vs AHI covers the difference in detail.

What does Medicare cover?

Medicare Part B covers Type I, II, III and IV sleep tests and devices for eligible patients, meaning those with clinical signs and symptoms of sleep apnea.⁵ Medicare covers Type I tests only in a sleep lab facility, and a doctor or other health care provider must order the sleep test.⁵

After the Part B deductible, the patient pays 20% of the Medicare-approved amount, with specifics depending on factors such as other insurance and whether the doctor accepts assignment.⁵ For the patient side of costs, see how much a home sleep study costs.

CPT coding for sleep testing may change under the CY2027 proposed rule. Our guide to the proposed 2027 sleep testing CPT codes covers that proposal.

Which patients need which type?

The AASM recommends polysomnography, or HSAT with a technically adequate device, for uncomplicated adults with signs and symptoms that indicate an increased risk of moderate to severe OSA.⁴ It recommends polysomnography rather than HSAT for patients with conditions that include significant cardiorespiratory disease, chronic opioid medication use, a history of stroke and severe insomnia.⁴

If a single HSAT is negative, inconclusive or technically inadequate, the guideline recommends polysomnography.⁴ The full criteria, including what the guideline means by uncomplicated, are in which patients are good candidates for a home sleep apnea test.

Wesper develops FDA-cleared home sleep testing medical devices and offers two levels of home sleep testing, Wesper Lab and Wesper Lite, on one platform. Wesper Lab uses two wearable patches on the chest and abdomen and measures airflow and thoracic and abdominal effort with no nasal cannula, and Wesper Lite is a PPG-based sleep test in a ring format. Both are indicated for adult use only, and multi-night testing comes standard.

Frequently asked questions

Is a home sleep apnea test the same as a Type III study?

The two terms come from different systems. CMS defines Type III by a minimum channel count, while the AASM defines home sleep apnea testing as unattended testing for OSA without determining sleep stage.^{1, 3}

Which types of sleep study monitor sleep stages?

Type I polysomnography is scored for sleep stages, and CMS describes Type II devices as monitoring sleep staging.^{1, 2}

Does Medicare cover home sleep tests?

Medicare Part B covers Type I, II, III and IV sleep tests and devices for people with clinical signs and symptoms of sleep apnea. Type I tests are covered only in a sleep lab facility.⁵

What does Medicare require for Type IV coverage?

Medicare covers Type IV devices that measure three or more channels, including airflow.¹

Is Level 4 the same as Type IV?

The two labels are often used for the same category. CMS writes it as Type IV and uses it for devices that do not meet all the criteria of a higher category.¹

For device and program details, visit our page on home sleep testing for clinics.

This article is for general education and is not medical advice. Talk with a licensed medical provider about your symptoms and testing options.

Sources

1. Centers for Medicare and Medicaid Services. National Coverage Determination 240.4.1: Sleep Testing for Obstructive Sleep Apnea. Effective March 3, 2009. cms.gov
2. American Academy of Sleep Medicine. Sleep study. Sleep Education. Reviewed September 2020. sleepeducation.org
3. American Academy of Sleep Medicine. AASM style guide for sleep medicine terminology. Updated November 2015. aasm.org
4. Kapur VK, Auckley DH, Chowdhuri S, Kuhlmann DC, Mehra R, Ramar K, Harrod CG. Clinical practice guideline for diagnostic testing for adult obstructive sleep apnea: an American Academy of Sleep Medicine clinical practice guideline. J Clin Sleep Med. 2017;13(3):479-504. aasm.org
5. Medicare.gov. Sleep studies. medicare.gov