Understanding Your Sleep Study Results: AHI Explained

The most important number in your sleep study report is your Apnea-Hypopnea Index (AHI). It counts how many times an hour your breathing stops or gets shallow during sleep. Your AHI, together with your symptoms and health, guides your treatment.

What is in your sleep study report?

After your sleep study, you'll get a report. It has numbers, measurements, and medical words that can feel overwhelming. Knowing what your AHI means helps you understand your diagnosis and treatment plan.

Oxygen levels, sleep efficiency, and sleep position data also matter. Your sleep specialist will explain your results and suggest a plan made for you.

What is AHI?

The AHI measures how many times per hour your breathing is disrupted during sleep. It counts two kinds of events:

• Apnea — Breathing stops completely for at least 10 seconds.
• Hypopnea — Airflow drops by at least 30% for at least 10 seconds. It comes with a drop in oxygen or a brief awakening (arousal).

To get your AHI, the total number of apneas and hypopneas is divided by the total hours of sleep.

AHI severity levels

• Normal — AHI less than 5. No significant sleep apnea.
• Mild — AHI 5-14. Some breathing problems. Treatment may be advised based on your symptoms.
• Moderate — AHI 15-29. Treatment is usually advised.
• Severe — AHI 30+. Treatment is strongly advised.

What other numbers are in your report?

• Oxygen nadir — The lowest blood oxygen level during sleep. Levels below 90% are a concern. Below 80% is severe.
• Oxygen desaturation index (ODI) — How many times per hour your oxygen drops by 3-4%.
• Sleep efficiency — The share of time in bed you actually spent asleep. Normal is above 85%.
• REM AHI — Your AHI during REM (dreaming) sleep, which is often worse.
• Supine AHI — Your AHI when you sleep on your back. It is often higher than when you sleep on your side.
• Arousal index — The number of brief awakenings per hour.
• PLM index — Periodic limb movements (leg movements that repeat) per hour.

How does AHI guide treatment?

Your AHI, your symptoms, and your overall health together decide the treatment plan:

• Mild OSA, or obstructive sleep apnea (AHI 5-14) — May be treated with lifestyle changes, positional therapy (sleeping off your back), or an oral appliance (a device worn in the mouth). CPAP may be advised if symptoms are significant. CPAP is a machine that blows air through a mask to keep your airway open.
• Moderate OSA (AHI 15-29) — CPAP is usually the first treatment. Oral appliances are another option.
• Severe OSA (AHI 30+) — CPAP or BiPAP is strongly advised. Inspire therapy may be an option for people who can't use PAP (positive airway pressure) comfortably.

Myth: A low AHI means I don't need treatment. Fact: Even mild sleep apnea (AHI 5-14) may need treatment if you have significant symptoms. These include daytime sleepiness, morning headaches, or risk factors for heart and blood vessel disease.