OSA can be diagnosed during a sleep study conducted either in a laboratory or at home. To qualify for a Medicare rebate for a home-based study, patients need to score 8 or more on ESS AND 5 or more on OSA 50 OR 3 or more on STOP-Bang.
OSA can be diagnosed during a sleep study or polysomnography (PSG) conducted either in a sleep laboratory or increasingly via a home-based study.
The pathway to having a sleep study can be through referral to a sleep or respiratory specialist who then organises the study or under certain criteria by direct referral from the GP. Reasons to consider referral to a sleep or respiratory medicine specialist are shown in the table below.
Table. Referral to a sleep or respiratory medicine specialist assessment requirements
A sleep specialist assessment is required if:
- Excessive daytime sleepiness (ESS ≥ 16)
- Sleepiness-related accident
- OSA and patient represents a significant driving risk
- OSA and high-risk occupation e.g., commercial driver, heavy machinery operator
- Severe morbid obesity (BMI ≥ 45 kg/m2)
- Neuromuscular or chest wall deformity
- Uncontrolled psychological or psychiatric disorders
- COPD (with FEV1/FVC ≤ 70% and FEV1 ≤ 50% predicted)
- Supplemental oxygen required
- Waking oxygen level ≤ 92%
- Serum bicarbonate ≥ 28 mmol/L
- Awake hypercapnia or sleep hypoventilation syndrome (e.g., CO2 ≥ 45 mmHg or SpO2 ≤ 90% for ≥ 30% of total sleep time on the diagnostic study)
- Other significant sleep, respiratory, or cardiac disorders
The gold standard test for diagnosing OSA is with in-laboratory full polysomnography (PSG) with a sleep scientist in attendance throughout the night. However, in-laboratory PSG is limited in its availability, labour intensive and costly, so increasing attention has been focused on home sleep study testing (set up initially by a sleep scientist and patient proceeds with the overnight test at home unattended, or where the patient is able to set it up themselves). Traditionally, sleep studies have been divided into four categories.
Table. Levels of sleep study relevant to OSA
- Level 1 Full polysomnography (PSG) in sleep laboratory, attended by sleep scientist, comprising ≥7 channels
- Level 2 Full PSG at home, unattended by sleep scientist, comprising ≥7 channels
- Level 3 Portable testing at home, attended or unattended by sleep scientist, comprising 3-6 channels
- Level 4 Portable testing at home, unattended by sleep scientist, comprising 1-2 channels
≥7 channels include airflow, oxygen saturation, respiratory effort, electrocardiography (ECG) and electroencephalography (EEG), limb movemen
3-6 channels include monitoring of breathing parameters without sleep assessment
1-2 channels include airflow, oxygen saturation, or heart rate
Choosing to order a sleep study at home has advantages (e.g. Increased patient comfort, shorter waiting time, avoids using hospital beds) and disadvantages (10% failure rate, patient or staff need to set up, no video recording made). A level 2 study is the most robust home study comprising ≥ 7 channels. In the correct clinical setting, this can produce equivalent results to a full in-laboratory diagnostic study. Level 3 or 4 home studies have more limited monitoring, between 1 to 4 channels. Level 3 and 4 studies have been shown to have reasonable diagnostic accuracy for confirming OSA in patients with a high pre-test probability of moderate-to-severe OSA without other significant medical or sleep comorbidities, and may be useful in improving access to diagnostic services, particularly in rural and remote regions. MBS reimbursement is currently unavailable for level 3 and 4 sleep study testing. Level 3 studies are being provided by some commercial sleep study providers, however, quality cannot be guaranteed in the absence of a professional accreditation process.
To help prioritise and reduce waiting lists, home studies may also be appropriate in some settings as a screening tool for patients with high pre-test probability of OSA (e.g. sleepy obese patients who snore and take antihypertensive drugs). Home-based tests (e.g. level 4 testing using two channels; oximetry and nasal pressure, e.g. ApneaLink) can be useful to rule in
OSA in these patients, but not to rule out OSA; the tests have high specificity and high sensitivity when compared to full PSG (level 1). Therefore, if there is a strong clinical suspicion of OSA and the limited channel study is negative, the diagnosis should not be excluded without an in-laboratory sleep study and specialist review.
Patients who require urgent in-laboratory assessment include those with unstable cardiovascular status (e.g. nocturnal angina or recurring cardiogenic pulmonary oedema), hypercapnic respiratory failure, high pre-test probability of OSA who are about to undergo major surgery, and history of significant drowsiness while driving.
The model of care for OSA is area specific; rural services may differ from urban services regarding access to a sleep physician and sleep laboratory (monitored polysomnography) and be more dependent on home-based sleep studies (unmonitored polysomnography, overnight monitoring of respiration, oxygen saturation, and pulse, or pulse and oximetry monitoring only).
Of note, to avoid conflicts of interest prescription of CPAP should not be affected by the financial interest in the selling of CPAP machines (Australasian Sleep Association. Best practice guidelines for the provision of CPAP therapy).