National Sleep Foundation

Chapter 3: Sleep-Related Breathing Disorders

Assessment and Diagnosis

OSAS should be suspected in patients who present with excessive daytime sleepiness (EDS), particularly if they are overweight and/or their bed partners have observed snoring, gasping, or episodes in which the person stops breathing.

If uncomplicated OSAS is suspected in adults, diagnosis with home sleep testing (and treatment with autotitrating CPAP) have been shown to have comparable outcomes to in-center management.1 2 3

If complicated sleep-disordered breathing (such as hypoventilation or central sleep apnea or in the presence of significant cardioresiratory disease) is suspected, referral to a sleep center is appropriate. Home sleep testing is not generally used for assessment in children.

Assessment of OSAS

Sleep-disordered breathing can be assessed by in-lab or out-of-center testing.

Assessment of OSAS at a sleep disorders center is primarily by polysomnography (PSG). A complete in-laboratory PSG includes:

  • Assessment of the patient’s apnea-hypopnea index (AHI), drops in O2 saturation, sleep quality, electrocardiogram, body position, limb movements, and the occurrence and severity of snoring (see Figure 3a).
  • An in-laboratory Continuous Positive Airway Pressure device (CPAP) titration may occur on the same night as the PSG, (a “split night study”) or on a subsequent study. The purpose of this study is to determine the amount of pressure (in cm H20) needed to keep the patient’s airway open.

For uncomplicated sleep apnea, home testing with autotitrating CPAP usually results in the same short-term outcomes. 4

Figure 3a: Polysomnographic recording of two episodes of obstructive sleep apnea. Note the lack of airflow despite the effort to breathe (ribcage and abdomen recording) during each event.

Diagnosis of OSAS

Diagnostic criteria for OSAS include an Apnea-Hypopnea Index (AHI) of five or more (> 5) ; apneas or hypopneas per hour of sleep with compatible symptoms, including sleepiness.

Although the diagnostic criterion for OSAS is an AHI of  equal to or greater than five, this is not absolute and there is no threshold where the AHI becomes definitively pathologic. Cutoffs of 5, 15, and 30 disordered-breathing events per hour indicate “mild,” “moderate,” and “severe” levels of OSAS, respectively. An AHI of 5 or less usually indicates that no treatment is needed, while an AHI of 15 and above usually indicates that treatment is required.  In addition, the degree and duration of oxygen desaturation are important determinants of OSAS’ severity.

Increasingly, research studies are basing assessment of apnea severity on the Oxygen Desaturation Index (ODI), which is the number of times per hour the oxygen saturation falls by 3 or 4 percent, or on the time spent with saturations below 90 percent.

This evidence is usually coupled with reports of EDS, insomnia, or sleep that is disturbed and/or not refreshing. 5

An initial sleep study is necessary to document the presence, and assess the severity of OSAS.


  1. Kuna ST, Gurubhagavatula I, Maislin G, et al., Noninferiority of functional outcome in ambulatory management of obstructive sleep apnea. Am J Respir Crit Care Med. 2011;183:1238-44.
  2. Antic NA, Buchan C, Esterman A, et al.  A randomized controlled trial of nurse-led care for symptomatic moderate-severe obstructive sleep apnea.  Am J Respir Crit Care Med. 2009;179:501-508.
  3. Chai-Coetzer CL, Antic NA, Rowland LS, et al., Primary care vs. specialist sleep center management of obstructive sleep apnea and daytime sleepiness and quality of life: a randomized trial. JAMA. 2013 Mar 13;309:997-1004.
  4. Kuna ST, Gurubhagavatula I, Maislin G, et al., Noninferiority of functional outcome in ambulatory management of obstructive sleep apnea. Am J Respir Crit Care Med. 2011;183:1238-44.
  5. Meoli AL, Casey KR, Clark RW, et al. Clinical Practice Review Committee. Hypopnea in sleep-disordered breathing in adults. Sleep. 2001;24:469-470.