AHI stands for apnea-hypopnea index, a number that tells you how many times per hour your breathing partially or completely stops while you sleep. An AHI below 5 is considered normal in adults. Anything at 5 or above indicates some degree of sleep apnea, and the higher the number, the more severe the condition.
How AHI Is Calculated
The number comes from a sleep study, either in a lab or at home. During the test, sensors track your breathing, oxygen levels, and brain activity. Technicians then count two types of events: apneas (moments when airflow stops completely for at least 10 seconds) and hypopneas (moments when airflow drops by at least 30% for 10 seconds or more, paired with a dip in blood oxygen of 3% or greater, or a brief awakening). Your AHI is simply the total number of these events divided by the hours you slept.
So if you had 120 events over 8 hours of sleep, your AHI would be 15. That single number becomes the primary way doctors classify how serious your sleep apnea is.
What the Severity Ranges Mean
The American Academy of Sleep Medicine breaks adult AHI scores into three tiers:
- Mild (5 to 14): Your breathing is disrupted 5 to 14 times per hour. Many people at this level snore heavily and feel somewhat tired during the day but may not realize anything is wrong.
- Moderate (15 to 29): Breathing interruptions happen 15 to 29 times per hour. Daytime sleepiness, difficulty concentrating, and morning headaches become more common.
- Severe (30 or higher): Your breathing is disrupted at least 30 times every hour, meaning roughly once every two minutes. At this level, oxygen levels can drop significantly throughout the night.
Children are held to a stricter standard. An AHI of 1 or higher is considered abnormal in kids 13 and younger, because even a few breathing disruptions per hour can affect a child’s development and behavior. For teenagers between 13 and 17, doctors may use either the pediatric or adult scale depending on the child’s size and development.
Why AHI Matters for Your Health
Untreated sleep apnea has been linked to a range of problems beyond poor sleep. The repeated drops in oxygen and the constant micro-awakenings put stress on your cardiovascular system over time. Research has connected untreated obstructive sleep apnea to hypertension, diabetes, stroke, daytime sleepiness, and reduced attention and cognitive function. Mood disorders and insomnia are also common.
That said, AHI alone doesn’t tell the whole story. A growing body of research shows that how far your oxygen drops during each event, known as the “hypoxic burden,” may be a stronger predictor of cardiovascular risk than the event count itself. Two people can have the same AHI of 20, but if one person’s oxygen barely dips while the other’s plummets repeatedly, their health risks differ substantially. One large study found that people with the highest hypoxic burden had roughly 2 to 3 times the risk of cardiovascular death compared to those with the lowest, even after adjusting for other health factors.
How AHI Affects Treatment Decisions
Your AHI score plays a direct role in whether you qualify for treatment and what your insurance will cover. Medicare, for example, covers CPAP therapy for adults with an AHI of 15 or higher. If your AHI falls between 5 and 14, coverage still applies, but you need documented symptoms: excessive daytime sleepiness, impaired thinking, mood problems, insomnia, or conditions like high blood pressure, heart disease, or a history of stroke.
Once you’re on CPAP or another treatment, the goal is to bring your AHI below 5. Most modern CPAP machines track your AHI nightly, so both you and your doctor can see whether the therapy is working. If your numbers aren’t dropping, it usually means the mask fit, pressure settings, or treatment approach needs adjusting.
Home Sleep Tests vs. Lab Studies
Many people now get their AHI from a home sleep test rather than spending a night in a sleep lab. Home tests are more convenient and less expensive, but they’re somewhat less precise. When researchers compared home devices to in-lab studies for detecting moderate sleep apnea (AHI of 15 or higher), home tests correctly identified 80% of people who had the condition and correctly cleared 83% of those who didn’t. That means about 1 in 5 people with sleep apnea could get a falsely normal result from a home test.
Home tests also tend to slightly underestimate AHI because they measure recording time rather than actual sleep time. If you spent an hour lying awake, the device still counts that hour in its calculation, which dilutes the number. If your home test result doesn’t match your symptoms, your doctor may recommend a full in-lab polysomnography for a more accurate picture.
Other Numbers on Your Sleep Report
Your sleep study results may include a few other metrics alongside AHI. The Respiratory Disturbance Index (RDI) counts the same apneas and hypopneas but also includes subtler breathing disruptions that don’t quite meet hypopnea criteria yet still wake you briefly. Your RDI will always be equal to or higher than your AHI. The Oxygen Desaturation Index (ODI) counts how many times per hour your blood oxygen drops by 3% or 4%, regardless of whether a scoreable breathing event triggered it. Together, these numbers give a more complete picture than AHI alone, especially for people whose AHI looks borderline but who still feel terrible during the day.