Sleep Study Explained: Home Sleep Test, Polysomnography and AHI
A sleep study diagnoses obstructive sleep apnoea. Learn home vs in-lab testing, the AHI severity scale, and CPAP thresholds.
A sleep study measures airflow, oxygenation and respiratory effort during sleep to diagnose obstructive sleep apnoea (OSA). Home sleep tests are first-line in high-probability adults; in-lab polysomnography is needed for complex cases. Severity is graded by the apnoea–hypopnoea index (AHI): mild 5–14/h, moderate 15–29/h, severe ≥ 30/h. CPAP is offered for symptomatic moderate/severe OSA or symptomatic mild with cardiovascular disease.
OSA is highly prevalent (up to 30% of middle-aged adults) and under-diagnosed. STOP-BANG (Snoring, Tired, Observed apnoea, Pressure, BMI, Age, Neck, Gender) triages screening: ≥ 3 = intermediate-high risk. NICE NG202 (2021) recommends home sleep testing (multi-channel: airflow, respiratory effort, SpO₂, heart rate, position) in high-probability adults; polysomnography (also includes EEG, EMG, EOG) is reserved for complex cases (central sleep apnoea, parasomnia, seizures, or discordant home study). Severity based on AHI (events/hour) or REI (Respiratory Event Index in home studies). Untreated moderate/severe OSA increases cardiovascular mortality, hypertension resistance, atrial fibrillation, stroke risk, and daytime accidents. CPAP is first-line — 4-hour nightly use improves symptoms and BP; adherence is challenging (~50% at 1 year). Alternatives: mandibular advancement devices (mild–moderate), positional therapy, weight loss, hypoglossal nerve stimulation (Inspire), and upper-airway surgery in selected cases.
- Screening tool
- STOP-BANG (≥ 3 intermediate–high)
- AHI severity
- Mild 5–14, moderate 15–29, severe ≥ 30
- First-line therapy
- CPAP (symptomatic moderate/severe)
- Home vs polysomnography
- Home first-line for high-probability adults
- Adherence
- 4 h/night improves outcomes
Home sleep test vs polysomnography
| Factor | Home | Polysomnography |
|---|---|---|
| Location | Own bed | Sleep lab |
| Channels | 4–7 (respiratory) | 16+ (adds EEG/EMG/EOG) |
| Cost | Lower | Higher |
| Best for | Uncomplicated OSA | Central apnoea, parasomnias, discordant home study |
Indications for sleep study
Habitual snoring + witnessed apnoea + daytime sleepiness.
Resistant hypertension, atrial fibrillation, or heart failure workup.
Assessment for bariatric surgery.
Occupational safety (HGV drivers, pilots).
Persistent excessive daytime sleepiness after other causes excluded.
- Excessive daytime sleepiness impairing driving — sleep clinic urgently.
- OSA + right-heart failure or resistant hypertension — combined cardiology/sleep referral.
- Central sleep apnoea + heart failure — specialist assessment.
OSA pathway
- 1STOP-BANG ≥ 3 + symptoms?Home sleep test.
- 2Complex or discordant home study?In-lab polysomnography.
- 3AHI ≥ 15 and symptomatic?CPAP.
- 4Mild OSA?Consider MAD, weight loss, positional therapy.
Related questions people ask
Frequently asked questions
- OSA is common and cardiovascularly hazardous.
- STOP-BANG triages risk.
- Home sleep testing is first-line for uncomplicated adults.
- AHI grades severity.
- CPAP is first-line for symptomatic moderate/severe OSA.
References
2 sources- NICE NG202Obstructive sleep apnoea/hypopnoea syndrome
UK national guideline.
nice.org.uk
- AASMClinical Practice Guidelines
American Academy of Sleep Medicine.
aasm.org
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