Whether you had a home sleep study or a full overnight
polysomnography (PSG) in hospital, this page explains the main numbers
on the report — and lets you enter your own scores for plain-language guidance.
This tool is for education only. It does not diagnose or treat any condition.
Always discuss your report with your sleep clinician or GP — scoring rules and
clinical context matter.
Home & full PSG
AHI — Apnoea–Hypopnoea Index
Average number of breathing pauses (apnoeas) and shallow-breathing events (hypopnoeas) per hour of sleep. The main figure used to grade obstructive sleep apnoea in adults.
Adult ranges: under 5 normal · 5–14 mild · 15–29 moderate · 30+ severe
Home studies may report REI (respiratory event index) — interpreted in a similar way.
Home & full PSG
ODI — Oxygen Desaturation Index
How often your blood oxygen drops by a set amount (often 3% or 4%) each hour. Closely related to AHI and linked to cardiovascular risk.
Higher ODI usually tracks with more severe sleep-disordered breathing. Your lab’s report should state the desaturation threshold used.
Home & full PSG
Lowest SpO₂ / time below 90%
The lowest oxygen saturation overnight, and how long levels stayed under 90%. Important for heart and lung risk, not only for “severity counts”.
Nadir under about 90% is common in OSA; prolonged time below 90% or very low nadirs need clinical review.
Full PSG mainly
Sleep onset latency
Minutes from “lights out” until you first fall asleep. Home studies often do not measure true sleep stages, so latency may be missing or estimated.
Rough guide: under 30 minutes is typical. Very short latency can mean high sleep pressure; long latency can fit insomnia or first-night effect in a lab.
Full PSG mainly
REM latency
Time from sleep onset to the first REM (dreaming) period. Used when narcolepsy or unusual sleep architecture is being considered.
Often around 60–120 minutes in healthy adults. Very short REM latency needs specialist interpretation.
Full PSG mainly
Sleep efficiency
Percentage of time in bed that was actually spent asleep (total sleep time ÷ time in bed × 100).
About 85% or higher is often considered good in adults. Lower values are common with insomnia, pain, or lab discomfort.
Full PSG mainly
Arousal index
Brief awakenings or EEG arousals per hour of sleep. Can rise with apnoeas, leg movements, noise or pain.
Many labs regard under about 10–20/hour as less concerning; higher values can explain unrefreshing sleep.
Full PSG (sometimes home)
Leg movements — PLMI
Periodic Limb Movement Index: stereotyped leg jerks per hour of sleep. Some home devices estimate movement; full PSG measures them more accurately with leg sensors.
Adults: PLMI under 15 is often treated as normal; 15+ may support periodic limb movement disorder if there are symptoms and other causes are ruled out.
Full PSG
Sleep stages (N1, N2, N3, REM)
How your night was divided between light sleep, deep sleep and REM. Only full PSG with EEG can stage sleep accurately.
Typical adult mix is roughly: little N1, about half N2, ~20% deep (N3), ~20–25% REM — but age and first-night effect change this.
Enter your report scores
Fill in the numbers from your written report. Leave blank any value you do not have — guidance only appears for what you enter.
