Sleep apnoea screening: what the wearables can and can't tell you

Obstructive sleep apnoea (OSA) is one of the most common (and most under-recognised) sleep disorders in adults. HypnoLaus, a Swiss population study of adults aged 40–85, found moderate-to-severe sleep-disordered breathing in 23.4% of women and 49.7% of men. OSA is widely undiagnosed.

What OSA actually is#

OSA is repeated partial or complete upper-airway collapse during sleep. Each event is an apnoea (full obstruction, 10+ seconds) or hypopnoea (partial obstruction with desaturation). The body responds with a brief arousal; the sleeper rarely remembers it. Multiply this by 30+ events an hour and you get fragmented sleep, repeated drops in blood oxygen, and chronic sympathetic activation overnight.

The metrics that matter clinically:

• AHI (Apnea-Hypopnea Index): events per hour. Mild: 5–15. Moderate: 15–30. Severe: 30+.
• ODI (Oxygen Desaturation Index): how often oxygen drops by ≥3% from baseline.
• Lowest SpO2: the deepest desaturation observed.

Signs worth taking seriously#

The classic triad: loud snoring, witnessed apnoeas, daytime sleepiness. Other red flags:

• Waking gasping or choking
• Morning headache or dry mouth
• Refractory hypertension
• Atrial fibrillation
• Treatment-resistant depression
• Stroke or transient ischaemic attack
• Type 2 diabetes: OSA is more common in this population

A partner who reports witnessing pauses in breathing is one of the most specific clues in clinical practice.

STOP-BANG screening#

The STOP-BANG questionnaire is the most widely used clinical screen. Eight yes/no items:

• Snoring loudly
• Tired during the day
• Observed stop breathing
• Pressure (high blood pressure)
• BMI >35
• Age >50
• Neck circumference >40 cm
• Gender male

Three or more positive = intermediate risk. Five or more = high risk. The screen is cheap, has reasonable sensitivity in primary care, and is used in NHS pathways.

What wearables can do#

Modern wearables with SpO2 sensors (Apple Watch, Garmin, Whoop, Oura) can flag overnight desaturation patterns. Apple Watch's Sleep Apnoea Notifications feature is FDA-cleared in the US (510(k) K240929, September 2024) and available in the UK; it's a notification feature, not a diagnosis. It uses accelerometer-detected breathing disturbances and recommends a clinical evaluation when patterns suggest OSA.

This is genuinely useful for surfacing undiagnosed cases. But it's not diagnostic.

What wearables can't do#

A consumer wearable cannot:

• Measure AHI directly
• Distinguish obstructive from central apnoeas
• Quantify hypopnoeas the way polysomnography does
• Replace a clinical sleep study

If a wearable flags possible OSA, the right next step is a GP appointment for referral to a sleep service. NHS pathways usually involve a home sleep study (Type III device) measuring oxygen, heart rate, airflow, and chest movement. In-lab polysomnography is reserved for complex cases.

Treatment overview#

For moderate-to-severe OSA, CPAP is the NICE-recommended first-line treatment. Adherence is the challenge — modern auto-titrating machines and well-fitted masks have improved tolerability substantially. Mandibular advancement devices are options for mild-to-moderate cases or CPAP-intolerant patients. Weight loss reliably improves OSA severity and is recommended alongside other treatments where applicable. Positional therapy helps the subset of patients with positional OSA.

We don't cover these in detail; they're clinical decisions made with a sleep service.

What we'd actually say#

If you snore loudly, are sleepy in the day, and have a STOP-BANG of 3+, see your GP and ask specifically about sleep apnoea. If a wearable has flagged a pattern, take that into the appointment — it's a useful artefact.

OSA is one of the few sleep conditions where treatment dramatically changes life: cognition, energy, BP, AF burden, and stroke risk all improve. Under-treatment in the UK is a public-health problem.