Sleep Study (Polysomnography)
An overnight test that records breathing, oxygen, heart rate and brain activity during sleep.
Quick Summary
To diagnose sleep apnoea and other sleep disorders.
Breathing pauses, oxygen drops, sleep stages and movements.
Avoid caffeine and alcohol; bring your usual nightwear.
Overview
Some studies are done at home with a simpler device.
The apnoea-hypopnoea index (AHI) measures severity.
What It Measures
AHI
Breathing pauses per hour.
Oxygen
Lowest levels at night.
How It's Performed
- 01
Setup
Sensors on head, chest, finger and nose.
- 02
Sleep
Sleep as normally as you can.
- 03
Removal
Sensors removed in the morning.
Reference Ranges
Note: Normal ranges vary by laboratory. Consult your report for the specific reference used.
| Parameter | Typical Range (Adult) | Units |
|---|---|---|
| AHI (normal) | Below 5 | events/hour |
Interpreting Results & Next Steps
Discuss with Doctor
Your doctor will explain the report and what happens next.
If values are High:
AHI 5–15 mild, 15–30 moderate, over 30 severe sleep apnoea.
Sources and further reading
Last updated 21 October 2026. For more detail, see these trusted health organisations.
- Sleep Study(opens in a new tab) · MedlinePlus, US National Library of Medicine