Booking a Sleep Test This Autumn and Choosing Between Overnight Oximetry and Full Respiratory Polygraphy

Overnight oximetry vs respiratory polygraphy in one paragraph

The overnight oximetry vs respiratory polygraphy question comes down to how much the recorder is allowed to see. Overnight pulse oximetry captures two signals: arterial oxygen saturation and heart rate. Home respiratory polygraphy captures at least four, adding nasal airflow, breathing effort, snoring and body position. NICE guideline NG202 (England and Wales, 2021) sets the order plainly, telling clinicians to "offer home respiratory polygraphy to people with suspected OSAHS", and only "if access to home respiratory polygraphy is limited, consider home oximetry". It is guidance for one health system, but the most explicit published statement of that hierarchy in Europe. Being handed an oximeter is usually a sign of a constrained clinic, not of a clinically equal option. Our explainer on nocturnal ventilatory polygraphy covers what that fuller recording involves.

That difference is not administrative. It decides what your result can prove, because an oxygen trace has no channel for airflow and none for the position of your body. If you are still weighing testing at home against a hospital night, the separate question of home testing versus a lab sleep study comes first.

What each recorder physically picks up

Start the overnight oximetry vs respiratory polygraphy comparison with hardware. Overnight pulse oximetry is a fingertip or wrist sensor reading oxyhaemoglobin saturation, reported as SpO2, plus your pulse. From that trace a clinician derives your nadir SpO2, your T90 (time below 90% saturation) and your oxygen desaturation index. It is a level 4 portable sleep study.

Home respiratory polygraphy, also called cardiorespiratory polygraphy, is a level 3 study. NICE defines it as "at least 4 channels such as oximetry, breathing rate, apnoeas and hypopnoeas, snoring and body position". In practice that means a nasal cannula pressure transducer or thermistor airflow sensor, thoracoabdominal effort belts using respiratory inductance plethysmography, a snoring microphone channel and a body position sensor, on top of the oximeter. Polysomnography, or PSG, adds EEG so sleep stages and arousals can be scored under AASM scoring criteria.

What the two tiers are called across Europe

France uses polygraphie ventilatoire nocturne and polysomnographie, with oxymetrie nocturne outside the pathway. Spain uses poligrafia respiratoria and oximetria nocturna domiciliaria, Germany separates ambulante Polygraphie from nachtliche Pulsoxymetrie, Italy says poligrafia cardio-respiratoria notturna, the Netherlands searches verschil polygrafie en polysomnografie, and Czech clinics say limitovana polygrafie.

Two things sleep-test guides get wrong about overnight oximetry vs respiratory polygraphy

Two errors repeat across the pages ranking for overnight oximetry vs respiratory polygraphy.

The first is treating "home sleep test" as one product. Guides compare home against laboratory, then stop. That hides the fork that decides your result: two signals against four channels. Nobody tells the patient which one is arriving in the post.

The second is leaving a negative result unexplained. Competitor pages end at "the test came back clear" as though the question closed there. NG202 says the opposite, in writing: "Consider respiratory polygraphy or polysomnography if oximetry results are negative but the person has significant symptoms." A clean oxygen trace in a symptomatic person is a step in the pathway, not an exit from it.

The blind spot that makes a clean oxygen trace misleading

Not every breathing event ends in an oxygen drop. An apnoea is a near-total stop in airflow, while a hypopnoea is a partial reduction. A hypopnoea can end because the brain briefly wakes you, restoring throat muscle tone, before saturation falls far enough to register. That is a respiratory effort-related arousal, or RERA. A night of them fragments sleep while the oxygen line stays flat.

In the Thorax validation of the British Thoracic Society criteria (1995), oximetry alone reached 100% specificity but only 31% sensitivity for sleep apnoea/hypopnoea syndrome. Twenty-two confirmed patients were missed, and they were the ones with low apnoea scores and high hypopnoea scores. The authors concluded that people with negative oximetry and symptoms should go on to multi-channel recording or polysomnography.

A cost analysis in Chest (1998) followed patients whose overnight oximetry came back normal. Seventeen of twenty-eight, or 61%, still had treatable conditions found on full polysomnography. The authors judged screening oximetry "not cost-effective because of poor diagnostic accuracy".

Upper airway resistance syndrome, or UARS, is invisible to an oximeter for the same reason. It is scored through arousals and the respiratory disturbance index, or RDI, which counts effort-related events the apnoea-hypopnoea index leaves out. If your complaint is unrefreshing sleep rather than witnessed pauses, this blind spot is aimed at you.

ODI and AHI are not the same number

An oximetry report hands you an oxygen desaturation index, the count of desaturations per hour at a 3% or 4% drop threshold (ODI3 or ODI4). The severity bands that decide your treatment sit on a different index. NICE NG202 (2021) defines mild OSAHS as an apnoea-hypopnoea index of 5 to under 15, moderate as 15 to under 30, and severe as 30 or more. Those are AHI thresholds.

How closely do the two agree? A 2022 analysis in Sleep Science found ODI matched AHI on severity classification in 87.32% of cases, and that an ODI above 20 gave 96.6% sensitivity with 69.6% specificity for severe obstructive sleep apnoea. Read that carefully. The ODI earns its keep as a rule-in signal at the severe end. It is weakest exactly where most home testers sit, in the mild and moderate band.

France states the threshold in its own words. The Assurance Maladie pathway describes the polygraphie ventilatoire nocturne as a recording of at least six hours covering ECG, respiratory movements, nasal airflow and finger-sensor oxygen saturation, and says an IAH above 30 means severe sleep apnoea. The authority quoted there is the Haute Autorite de Santé, not the AASM. Standalone nocturnal oximetry is not presented as a diagnostic route at all, so a consumer oximeter bought online in France has no path into a reimbursed CPAP prescription. If a report is already in your hands, our guide to what an AHI score actually means decodes the headline figure.

Position and snoring, the two channels that shape your options

An oximeter cannot tell you whether you were on your back. Positional obstructive sleep apnoea, or POSA, is the pattern where breathing events cluster while you lie face-up and ease off once you turn. That one missing channel closes off a whole category of treatment discussion, and it matters most in the mild band.

Chest (2005) found positional sleep apnoea in 49.5% of patients with mild OSA at an AHI of 5 to 15, in 19.4% of moderate cases and in only 6.5% of severe ones. The European HypnoLaus cohort reported in Sleep Medicine (2018) analysed 1,719 subjects with at least thirty minutes in both supine and non-supine positions: positional OSA appeared in 53% of all subjects and 75% of those with OSA, with exclusive positional OSA in 36% of OSA subjects, which the authors said suggested a large proportion could be treated with positional therapy.

None of this is rare. Home polysomnography in 2,121 Lausanne adults aged 40 to 85 found an AHI of 15 or more in 23.4% of women and 49.7% of men (The Lancet Respiratory Medicine, 2015).

The snoring microphone channel does similar work. It separates a snoring-dominant night from silent obstruction, and it decides whether your report can support a discussion of positional therapy or a mandibular advancement device, or only CPAP titration. REM-related sleep apnoea sits one tier higher again. Spotting it means knowing your sleep stage, so only polysomnography can confirm it. Neither an oximeter nor a polygraph stages sleep.

Who should decline the cheap test outright

The overnight oximetry vs respiratory polygraphy choice is not equally weighted for everyone. One group should not accept an oximeter as their diagnostic test, and no consumer page says so. NICE NG202 warns that oximetry alone "may be inaccurate for differentiating between OSAHS and other causes of hypoxaemia in people with heart failure or chronic lung diseases".

The logic is simple. An oximeter sees saturation fall but cannot say why. In COPD, low overnight saturation may reflect the lung disease rather than an obstructed upper airway. That is the COPD-OSAHS overlap syndrome NG202 covers in the same guideline, alongside obesity hypoventilation syndrome, where sustained hypoventilation rather than discrete events drives the picture. Without airflow and effort channels, the causes are not separable.

Failed nights and the comparison nobody has run

Home kits fail. The 2026 NIHR Health Technology Assessment of home-testing devices for OSAHS reported sensitivity generally between 80% and 100%, specificity from 25% to 100% with many estimates in the 70% to 80% range, and test failure rates from 0% to 18%. A sensor slips, a belt loosens, and the night is unusable.

The same review made a quieter finding that reframes the decision: no studies compared novel home devices against home-based pulse oximetry. The tier European patients are steered towards on waiting-list grounds is the comparator nobody has benchmarked. When a clinic says the oximeter is just as good, ask what it was compared against.

How to choose between overnight oximetry vs respiratory polygraphy this autumn

Use this sequence.

On cost, the European evidence favours the fuller home test. In a Spanish multicentre randomised study of 366 patients (2013), managing suspected OSA with polysomnography for everyone cost 18% more than a home respiratory polygraphy pathway, for equal diagnostic and therapeutic decision efficacy. A companion trial placed home polygraphy protocols at 64% to 69% of the cost of polysomnography. Polygraphy became the European first-line test on economics, not convenience.

1. Keep your usual schedule and your usual room on the test night.
2. Do not start any new sleep device, appliance or medication beforehand.
3. Note alcohol, late meals and your usual sleeping position on the diary card.
4. Ask for the full report, not the summary letter, and check which index it states.

Where a nasal stent fits after the result, not before it

Devices belong after diagnosis, not inside the test decision. Back2Sleep is a CE-certified Class I soft silicone intranasal stent from a French company in Paris that keeps the nasal airway open during sleep. It is for snoring and mild-to-moderate obstructive sleep apnoea, needs no prescription, no electricity and no tubing, and the starter kit contains four sizes at around EUR 44.90. It does not treat severe OSA and does not replace CPAP where CPAP is indicated.

The link to this article is narrow. Whether a nasal appliance is even a sensible conversation depends on knowing your pattern is snoring-dominant, positional and mild-to-moderate. Those are exactly the facts the snoring channel, the body position sensor and an airflow-based AHI supply. An oximetry-only report cannot, so accepting two channels narrows what anyone can responsibly discuss with you afterwards.

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