CPAP tools
AHI Calculator
The apnea hypopnea index (AHI) is the number of apneas (breathing pauses) plus hypopneas (partial reductions in breathing) per hour of sleep. It is the main number used to grade obstructive sleep apnea severity. Enter the event counts from a sleep study report, or check the AHI your CPAP shows, to see how it is classified.
How it works
AHI = (apneas + hypopneas) / hours of sleep. Adult bands: under 5 normal, 5 to under 15 mild, 15 to under 30 moderate, 30 or more severe. Commonly used pediatric bands: under 1 normal, 1 to under 5 mild, 5 to under 10 moderate, 10 or more severe.
Example
60 apneas and 50 hypopneas over 6.5 hours of sleep: 110 / 6.5 = 16.9 events per hour, moderate range in an adult.
Assumptions and limits
- This is a screening and education aid, not a diagnosis. Only a clinician, usually with a sleep test, can diagnose a sleep disorder.
- A home sleep apnea test divides by recording time rather than measured sleep time, which can underestimate the true AHI; that figure is sometimes called the REI.
- How hypopneas are scored (3 percent oxygen drop or arousal under the AASM recommended rule, or 4 percent oxygen drop under the rule Medicare uses) changes the AHI.
- The AHI your CPAP reports is the machine's own estimate of residual events, not a diagnostic study result. Values under 5 are a common treatment goal.
- Pediatric cutoffs vary somewhat between sources, and diagnosis in children also weighs symptoms.
Frequently asked questions
What is a good AHI on CPAP?
Many clinicians aim for a machine reported AHI under 5 events per hour. If yours is higher or rising, or you still feel unrefreshed, tell your sleep clinician; the pressure, mask fit or the type of events may need a look.
What is the difference between an apnea and a hypopnea?
In adults, an apnea is a drop in airflow of at least 90 percent for at least 10 seconds. A hypopnea is a drop of at least 30 percent for at least 10 seconds with an oxygen drop or an arousal from sleep.
Why do children have lower cutoffs?
Healthy children rarely have breathing events during sleep, so even an obstructive AHI of 1 or more per hour is considered abnormal in pediatric sleep scoring.
What AHI does Medicare require to cover CPAP?
Under the Medicare coverage policy for PAP devices, an AHI or RDI of 15 or more, or 5 to 14 with certain symptoms or conditions such as excessive sleepiness, insomnia, hypertension, heart disease or a history of stroke, qualifies.
Sources
Tools and screening scores are general information. They cannot diagnose or rule out a sleep disorder. Read our medical disclaimer.