If sleep apnea is suspected after evaluating a patient, some form of sleep study is indicated to establish a diagnosis. Currently, an overnight in laboratory sleep study ( polysomnography) is a commonly used test for diagnosing sleep apnea. It requires an overnight stay in a sleep laboratory and includes evaluation of sleep staging, airflow and ventilatory effort, arterial oxygen saturation, electrocardiogram, body position, and periodic limb movements.

Polysomnography, however, is often not readily available, is uncomfortable for the patient, and is generally expensive (usually over $1000 per test), often requiring extensive time by patient and physician office in obtaining insurance authorization.. In addition, the results of polysomnographic sleep studies can vary significantly, due to the subjective nature of interpretaion).

Pulse oximetry alone has also been used for diagnosis. Unfortunately studies have shown that as a stand-alone test, oximetry only provides moderate sensitivity and specificity. A review of 12 studies (1784 patients) of oximetry alone found an average sensitivity of 87% and average specificity of only 65%.

Attempts have been made to monitor sleep at home, ranging from reduced channel PSG administered by technician, to self-contained devices which the patients administer themselves. Technician-administered home studies are usually reserved for patients who are unable to travel to a sleep facility and are complex and expensive to administer. Some self-administered devices have proven difficult to use and costly to maintain. Simpler devices have not been validated and/or do not meet third party reimbursement qualifications.

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The results of a sleep study will show both the type of sleep apnea, and provide a number of measures of its severity. The Apnea Index (AI) is the number of apneas per hour. Hypopnea is defined as a decrease in airflow of 50% or more (without complete cessation) for more than ten seconds accompanied by a drop in oxygen saturation of 2-4 percent, and the Hypopnea Index (HI) is the number of hypopneas per hour. Finally, the Apnea/Hypopnea Index (AHI) is the sum of AI and HI. The exact definition of sleep apnea in terms of the AHI was established by the American Academy of Sleep Medicine Task Force (Sleep 1999;22:667–689). Normal is AHI 0-5, mild 5-15, moderate 15-30, and severe 30+.

The degree and frequency of oxygen desaturations may also be an important parameter, particulary in patients with cardiovascular compromise. In general, most clinicians use a subjective mild/moderate/severe classification if referring to oxygen desaturations.

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