What Is AHI? Your Apnea-Hypopnea Index Explained

May 27, 2026·6 min read

Educational content, not medical advice. Ranges and clinical categories in this article come from the American Academy of Sleep Medicine and other published guidelines. Only your sleep specialist can interpret your specific numbers and recommend treatment. Full terms.

AHI — the Apnea-Hypopnea Index — is the number of times per hour your breathing was interrupted during sleep. It's the single most important metric for diagnosing and managing sleep apnea, and your CPAP machine reports it every morning. Here's what the number actually means.

The literal definition

AHI counts two specific events:

• Apnea — a complete pause in breathing lasting at least 10 seconds
• Hypopnea — a 30% or greater reduction in airflow lasting at least 10 seconds, paired with either a drop in blood oxygen or a brief arousal from sleep

Total events ÷ hours of sleep = AHI. If you slept 7 hours and had 14 events, your AHI is 2.0.

The clinical ranges (American Academy of Sleep Medicine)

These categories come from the AASM and are what your sleep doctor uses to interpret your sleep study results. Under 5 is what untreated, non-apnea adults typically experience.

"Diagnosed" AHI vs "CPAP" AHI

There are two AHI numbers in your life, and they measure different things:

Diagnosed AHI — The number from your in-lab sleep study or home sleep test, taken before treatment. This is the number that put you in mild / moderate / severe.

Residual AHI (a.k.a. CPAP AHI) — The number your CPAP reports each night. It's how often you still had events despite the CPAP delivering pressurized air. The goal of therapy is to drive this number below 5.

So someone diagnosed with severe sleep apnea (AHI 40+) can have a residual AHI of 1.5 on CPAP — the diagnosis doesn't change, but the therapy is working. The residual is what you watch every morning.

What a "good" CPAP AHI looks like

The typical clinical target for residual AHI on CPAP is under 5, with under 2 often considered well-controlled. If your residual AHI is consistently above 5, that's a good conversation to bring up at your next sleep appointment. Common topics in that conversation include:

• Whether the pressure setting is still appropriate
• Mask leak reducing effective pressure
• Comorbid factors (positional apnea, central events, REM-related events)
• Whether you're using the machine for enough of the night

Your sleep specialist is the right person to interpret these for your situation.

One bad night doesn't mean anything — AHI can swing significantly night to night. Here's why that happens. Look at 7-day and 30-day averages, not single-night spikes.

How accurate is your CPAP's AHI?

It's a useful number but not laboratory-grade. CPAP machines detect events through pressure and flow sensors in the air circuit — they can't see blood oxygen drops or EEG arousals the way a sleep lab does. In practice:

• Your CPAP catches obstructive apneas well
• It estimates hypopneas reasonably
• It may miss central events (where your brain temporarily stops sending the "breathe" signal)
• It often over-reports events during the first 30 minutes of sleep when your breathing is unsettled

A 1-2 point gap between your CPAP's estimate and a sleep lab's measurement is normal. What matters is the trend, not the absolute number.

Why log it daily?

Your sleep specialist sees you every 6–12 months. Between visits, only you know whether your numbers are trending well. A daily AHI log lets you:

• Catch slow upward drift (often a sign your mask cushion is wearing out)
• Connect bad nights to causes — alcohol, allergies, weight changes, mask issues
• Share a 30/90-day history with your doctor instead of a vague "I think it's been higher"
• Notice if a new medication or sleep-position change improved things

The ResMed myAir and Philips DreamMapper apps will store your CPAP's AHI history natively, but they don't let you add context (notes about the night, recent equipment changes, etc.) or work cross-brand if you switch machines.

FAQ

Is AHI 7 dangerous?

An AHI of 7 falls in the AASM's mild range. Research has linked untreated apnea to a range of outcomes including daytime sleepiness and cardiovascular concerns, but interpreting what AHI 7 means for any specific person is a clinical question. If your residual AHI on CPAP is consistently around this level, your sleep specialist can advise whether and how to adjust therapy.

What's a good AHI for a child?

Pediatric AHI thresholds and clinical criteria differ substantially from adult ones. A pediatric sleep specialist is the right person to interpret a child's sleep study results.

Can I have apnea with an AHI under 5?

Yes. UARS (upper airway resistance syndrome) involves arousals from partial airway obstruction without meeting the threshold for hypopnea. Sleep studies that look for RDI (respiratory disturbance index) catch these.

Why is my AHI worse on weekends?

Most commonly: alcohol relaxes airway muscles, and irregular sleep schedules disrupt the deeper sleep stages where CPAP works best. Try logging your AHI alongside your nightly habits to spot patterns.