Levels of Sleep Studies (by Dr Juan Mulder)

Diagnostic sleep studies

There are four levels of sleep studies available within the Australian context. It's important that we have some understanding of these when interpreting results.

Level 1

Most are aware of level 1 sleep studies, which are historically seen as the gold standard. This is usually done in a laboratory or in-house and attended by a sleep technician. This allows accurate data because the sleep technician can ensure the integrity of the data throughout the night. Level 1 studies are also required for CPAP review and assessment of somnolence or fitness to drive. They can be uncomfortable studies because they are done in a new environment. They also are not useful if a patient sleeps during the day and is awake at night.

Level 2

Level 2 studies have become increasingly popular because they allow clients to bypass a hospital, reduce cost, and speed up access. This is mostly used as a diagnostic tool for sleep apnoea and restless legs, but not adequate for parasomnia or more complex sleep disorders. Nowadays, some of the equipment can be used with CPAP or APAP machines to ascertain the effectiveness of therapy.

Both level 1 and 2 are Medicare reimbursed if the patient has an Epworth Sleepiness Scale Score of equal to or more than 8 and a STOP BANG equal to or more than 4. Otherwise, the need for the test first has to be assessed by a sleep physician.

Thus enter level 3 and level 4 studies.

Level 3

Level 3 studies usually measure breathing parameters but not sleep (brain EEG parameters). Some of the known devices are the ARES Watermark, Watch PAT, and Resmed Apnoea Link.

There are more devices than these three, but these seem to be the most often utilized.

The Watch PAT: This device measures peripheral arterial tone and uses it as a marker for sleep staging. This is worn on the hand. There has been a meta-analysis published on it. Disadvantages of this technology include the inability to differentiate between different types of sleep apnea (central, mixed, or obstructive). Use of PAT may also be limited by certain medications and diseases. Most articles reviewed in this study used stringent criteria to exclude patients with diabetes mellitus, peripheral neuropathy, vasculopathy, bilateral sympathectomy, and cardiac disease, and those taking α-adrenergic receptor–blocking agents.

ARES Watermark: This device is worn on the forehead and incorporates nasal airflow, pulse rate, snoring, head position, differentiates REM from NREM, actigraphy, and AHI/RDI. This does not measure parasomnia or restless legs. There have been at least two validation studies.

Resmed Apnoea Link: This device is worn around the chest. It records five channels of information: respiratory effort, pulse, oxygen saturation, nasal flow, and snoring. Validation has been done as well. Manually scoring the sleep staging seems to provide better results.

Level 4

Level 4 studies have one to two signals, but basically focus on pulse oximetry. They are very limited and pick up sleep apnoea in moderate to high-risk groups. They tend to underscore sleep apnoea severity and miss all the other sleep disorders.

Also, it makes sense to compare a test result to a similar test result. Thus, if a sleep study was done as a level 2, then the review study should be at least a level 2. A level 3 or 4 is more likely to provide falsely reassuring results.

Disclaimer: The material and information contained in this blog are relevant to the time it was written, for general purposes and in addition to what was provided for patients during their consultation. You should not rely upon the material on this website as a basis for decision-making.

Diagnosis of Obstructive Sleep Apnea by Peripheral Arterial Tonometry. Meta-analysis. Sreeya Yalamanchali, MD1; Viken Farajian, MS1; Craig Hamilton, MBChB1; et al Thomas R. Pott, MD1; Christian G. Samuelson, MD1; Michael Friedman, MD1,2. JAMA Otolaryngol Head Neck Surg. 2013;139(12):1343-1350. doi:10.1001/jamaoto.2013.5338

Validation study of a portable monitoring device for identifying OSA in a symptomatic patient population. To KW1, Chan WC, Chan TO, Tung A, Ngai J, Ng S, Choo KL, Hui DS. Respirology. 2009 Mar;14(2):270-5. doi: 10.1111/j.1440-1843.2008.01439.x. Epub 2008 Dec 11.

Validation of a Self-Applied Unattended Monitor for Sleep Disordered Breathing. Indu Ayappa, Ph.D.; Robert G. Norman, Ph.D.; Vijay Seelall, M.D.; David M. Rapoport, M.D. JCSM, 2008

Validation of the ApneaLink™ for the Screening of Sleep Apnea: a Novel and Simple Single-Channel Recording Device. Milton K. Erman, M.D.1; Deirdre Stewart, Ph.D.2 ; Daniel Einhorn, M.D.3 ; Nancy Gordon, M.S.4; Eileen Casal, R.N., M.N.5. JCSM 2007

Sleep Breath. 2017 Sep;21(3):799-807. doi: 10.1007/s11325-017-1532-3. Epub 2017 Jul 1. Validation of ApneaLink™ Plus for the diagnosis of sleep apnea. Cho JH1, Kim HJ2.