Testing Standards for Obstructive Sleep Apnea
Obstructive sleep apnea (OSA) is a commonly undiagnosed chronic condition. Studies suggest that moderate to severe OSA may contribute to the development of systemic hypertension, arrhythmias and cardiovascular disease. In addition, untreated OSA is associated with an increased risk of motor vehicle accidents.
The Gold Standard: Polysomnography
Guidelines developed in 2014 by the American College of Physicians include a recommendation that patients with daytime sleepiness and snoring, witnessed apneas or other sleep disturbances undergo a sleep study, preferably polysomnography (PSG). According to the recommendations, physician assessment should include evaluation of risk factors, comorbidities and common presenting symptoms for OSA. Although a PSG performed in a sleep laboratory is the "gold standard" for diagnosing OSA, it is resource-intensive and expensive and patients must spend the night under observation.
Home Sleep Testing
In the absence of PSG, the recommendation suggests portable monitors also may be used for a home sleep test (HST) to diagnose OSA in carefully selected patients. There are several types of portable devices. The most common is a "type III" device which measures between four and seven physiologic parameters typically including snoring, body position, air flow, respiratory effort, heart rate and oxygenation. Importantly, sleep variables, including sleep stages, sleep efficiency and continuity are not measured by these devices. A diagnosis of OSA can be made on the basis of a thorough clinical evaluation coupled with a sleep test with one of these devices.
A positive diagnosis is established if the apnea-hypopnea index as measured by the portable device is 15 or more (15 apneas or hypopneas an hour) or if AHI is between 5 and 14 and the patient has documented symptoms of one or more of the following: excessive daytime sleepiness, insomia symptoms, waking up with breath holding, gasping or choking, impaired cognition, mood disorders, hypertension, ischemic heart disease, atrial fibrillation, type 2 diabetes or a history of stroke.
The American Academy of Sleep Medicine recommends that HSTs be used only in patients with a high pretest probability for moderate to severe OSA and without serious comorbidities, such as cardiopulmonary or neuromuscular disorders, or in whom other sleep disorders are not a consideration. Furthermore, patients felt to be candidates for HSTs should have a consultation with a sleep trained provider to review their sleep history and to ensure that they are a good candidate for HST. The National Coverage Determination specifies that the home study must be ordered and supervised by the treating provider. It also limits the initial coverage of CPAP to a 12-week trial period.
HSTs do not use EEG electrodes to positively determine when a patient is asleep. The test is scored from "start to stop" compared to in-lab studies, which record the actual sleep portion of the test. This and other factors, such as sensors falling off or poor airflow signals, increase the risk of false-negative results with the HST. An HST is best for "ruling in" OSA, but not for ruling it out. Patients with a non-diagnostic HST are advised to undergo the more comprehensive in-lab PSG to more definitively assess for sleep-disordered breathing.
HSTs may be considered for home-bound patients, the elderly, or those with chronic illness who require specialized care, such as a nurse or family member spending the night. It also may be beneficial for patients who live far from sleep centers who have trouble arranging time out of their schedules or who face expensive transportation costs. While the "gold standard" for objective assessment of OSA is laboratory-based PSG, choosing an HST may be preferable in carefully selected patients. Currently, HSTs are best suited for patients with a high clinical index of suspicion for OSA and few comorbidities. Patients with low or intermediate levels of clinical suspicion, significant comorbidities or who present with atypical clinical features, may best be assessed initially by full PSG studies. HSTs should not be ordered in patients suspected of having insomnia, restless legs, narcolepsy or other parasomnias.