Updated 8 March 2026 · By Andy Leleux, sleep technologist
The route to a diagnosis, step by step
See your GP
Your GP is the starting point. Describe your symptoms: tiredness, snoring, sleepiness. They can run a questionnaire with you (Epworth, STOP-BANG) and refer you to a specialist if needed.
Ask whoever shares your bed to describe what you do at night. What they have noticed is valuable to the doctor.
An appointment with a pulmonologist or another sleep specialist
Your GP will usually refer you to a pulmonologist, an ENT specialist or a neurologist trained in sleep medicine. That specialist reviews your file and prescribes the right sleep study.
The sleep study (respiratory polygraphy or polysomnography)
This is the test that settles it. There are two kinds: respiratory polygraphy, which you can do at home, and polysomnography, done in a sleep center and more thorough. Both measure your AHI.
Results and treatment plan
Based on your AHI and your symptoms, the specialist proposes a treatment. If CPAP is indicated, the NIHDI convention can be opened so that it is reimbursed.
The sleep studies explained
Illustration being redrawn
Two panels: respiratory polygraphy at home (3 sensors) against polysomnography in a center (EEG + EOG + EMG + sensors)
polygraphie-vs-polysomnographie · 1000×500px · medical-diagram
Respiratory polygraphy
At homeIt records mainly airflow, blood oxygen saturation, and chest and abdominal movement. Enough in most cases.
Advantages
✓ Can be done at home
✓ More comfortable for you
✓ Costs less
✓ Results come back quickly
Limitations
− Fewer measurements
− Can underestimate the AHI
− Nobody is watching in real time
Polysomnography
In a sleep centerIt adds the EEG (brain activity), the EMG (movement), the ECG and your sleeping position. The gold standard for diagnosis.
Advantages
✓ The complete test
✓ Measures the stages of sleep
✓ Best for complex cases
✓ Medical supervision
Limitations
− A night away from home
− Longer to get an appointment
− A less natural setting
What a night in a sleep center is like
If your doctor prescribes a polysomnography, here is what actually happens, from admission to results.
Getting ready
- Bring comfortable nightwear (loose pajama bottoms are best: sensors go on your legs)
- Bring your toiletries (soap, shampoo, a towel: you will need to wash the electrode paste out)
- Bring the medication you usually take in the evening
- No nail polish and no false nails (an SpO₂ sensor is clipped to your finger)
- Remove make-up from your face and neck before you arrive
- You may be asked for a two-week sleep diary: bring it with you
Admission and settling in
- You are welcomed at the agreed time: be punctual, the preparation takes a while
- A light evening meal is often provided (or bring what you normally eat)
- You fill in a questionnaire about your sleep and your habits
- A baseline ECG may be recorded
Fitting the sensors (painless)
- EEG: electrodes stuck to the scalp with conductive gel, to measure the stages of sleep
- EOG: electrodes near the eyes, to measure eye movement (this is how REM sleep is spotted)
- EMG: electrodes on the chin and the legs, to measure muscle tone and movement
- ECG: electrodes on the chest, to measure heart rhythm
- Respiratory belts around the chest and the abdomen
- A nasal and/or oral airflow sensor
- A pulse oximeter on your finger, to measure blood oxygen saturation
- A microphone at the neck, to record snoring
- An infrared camera in the room (only with your consent, given beforehand)
Recording while you sleep
- You sleep on your own, in a single room
- A technologist watches every signal in real time from the control room
- You can get up to go to the bathroom: the cables are long enough
- Most patients do fall asleep despite the sensors: your brain adapts on its own
- The aim is to record at least six hours of sleep
Waking up and going home
- The electrodes come off (it does not hurt: the paste can leave the skin slightly red for a day)
- Plan on washing your hair thoroughly: the EEG paste takes several washes to come out
- You go home after breakfast
Going through the results
- The doctor reads the full report: hypnogram (your sleep architecture), AHI, oxygen levels, body position and more
- One night is usually enough for a reliable diagnosis
- Your health insurance fund covers this once a year (barring an exceptional medical reason)
Making sense of your result: the AHI
The AHI (apnea-hypopnea index) is the number of apneas plus hypopneas per hour of sleep. It is the central measure in the diagnosis.
Mild apnea
Moderate apnea
Severe apnea
Fewer than five events an hour in an adult is within the normal range.
The NIHDI convention: reimbursement in Belgium
In Belgium, CPAP treatment is reimbursed by the NIHDI, the National Institute for Health and Disability Insurance (INAMI/RIZIV), through a specific convention, provided you meet the clinical criteria.
Who can enter the CPAP convention:
An AHI of 15 or more (moderate to severe apnea), or
An AHI of 5 or more together with significant symptoms (sleepiness, high blood pressure and the like)
A diagnosis confirmed by respiratory polygraphy or polysomnography
An initial prescription by a pulmonologist or an accredited doctor
Note: The NIHDI convention comes with regular follow-up: your usage is checked and the agreement is renewed every year. A NIHDI-accredited provider is required to set the equipment up. The rules can change: ask your doctor what applies today.
Frequently asked questions
Prochaine étape
What does the night of the test actually involve?
What really happens: the preparation, each sensor and what it measures, the biocalibration, the night itself, the morning, and why a second night is often needed.
Prochaine étape
Is your AHI 15 or more? Here is what comes next
The NIHDI CPAP convention is what gets your device reimbursed. Costs, timings, the four-hour rule: it is all explained.
Sources
- Qaseem A, et al. Diagnosis of Obstructive Sleep Apnea in Adults: ACP Clinical Practice Guideline. Ann Intern Med. 2014;161(3):210-20.
- Kapur VK, et al. Clinical Practice Guideline for Diagnostic Testing for Adult OSA: AASM Guideline. J Clin Sleep Med. 2017;13(3):479-504.
- Lastra AC, et al. Diagnosis and Treatment of Obstructive Sleep Apnea. JAMA Intern Med. 2025.
- Gottlieb DJ, Punjabi NM. Diagnosis and Management of Obstructive Sleep Apnea. JAMA. 2020;323(14):1389-1400.
- Yeghiazarians Y, et al. Obstructive Sleep Apnea and Cardiovascular Disease: AHA Scientific Statement. Circulation. 2021;144(3):e56-e67.
