Sleep apnea is diagnosed through a sleep study that measures how many times your breathing stops or slows per hour while you sleep. That number, called the apnea-hypopnea index (AHI), is the single most important metric in confirming the diagnosis and determining severity. But before you get to a sleep study, there’s usually a screening process involving questionnaires, a physical exam, and sometimes a referral.
Screening and Risk Assessment
Most people start the diagnostic process by describing symptoms to their primary care doctor: loud snoring, waking up gasping, daytime sleepiness that doesn’t improve with more sleep, or a bed partner noticing pauses in breathing. From there, your doctor will typically use a structured screening tool to estimate your risk level before ordering a sleep study.
The most widely used screening tool is the STOP-Bang questionnaire, an eight-item checklist covering snoring, tiredness, observed breathing pauses, high blood pressure, BMI, age, neck circumference, and sex. A score of 3 or higher flags you as at risk. In validation studies, that cutoff caught 84% of all sleep apnea cases, 93% of moderate cases, and 100% of severe cases. Scores of 6 or above carry roughly a 75% probability of moderate to severe sleep apnea and typically prompt faster evaluation.
Your doctor will also examine your throat and airway. One common assessment is the Mallampati score, which rates how visible the back of your throat is when you open your mouth wide. The scale runs from I (wide open, easy to see) to IV (almost completely blocked by the tongue). People with a class IV score tend to have larger tongues, thicker necks (about 43 cm on average versus 40 cm in class II), and significantly more severe apnea events per hour. A large neck circumference on its own, generally above 17 inches in men or 16 inches in women, is considered a risk factor.
In-Lab Sleep Study (Polysomnography)
Polysomnography is the gold-standard diagnostic test. You spend a night at a sleep lab, usually in a private room designed to feel more like a hotel than a hospital. A technologist attaches sensors before you go to sleep, then monitors your data in real time from another room.
The sensors track a surprisingly long list of signals: brain waves (via EEG), eye movements, heart rate, breathing pattern, blood oxygen level, body position, chest and belly movement, limb movement, and snoring. Together, these readings let the technologist and sleep physician see exactly what happens each time your airway closes or your breathing weakens. Brain wave data shows which sleep stage you’re in when events occur, which matters because apnea often worsens during deeper sleep and REM sleep.
A single night is usually enough. Medicare and most private insurers cover one diagnostic polysomnogram without much pushback, as long as your symptoms and screening results support the need. If a second session is claimed, your insurer will typically require additional documentation explaining why the first study wasn’t sufficient.
Home Sleep Apnea Testing
Not everyone needs to sleep in a lab. The American Academy of Sleep Medicine recommends home sleep apnea testing as an alternative for adults who show signs of moderate to severe obstructive sleep apnea and don’t have other complicating conditions like heart failure, chronic lung disease, or suspected central sleep apnea.
A home test uses a simplified device you pick up from your doctor’s office or receive by mail. It typically measures airflow through a nasal sensor, blood oxygen via a finger clip, and chest movement with an elastic belt. What it doesn’t measure is brain activity, so it can’t tell which sleep stage you’re in or confirm how long you actually slept. This means home tests can underestimate severity: if you were awake for two hours but the device assumed you were sleeping, your events-per-hour count will be diluted.
If a home test comes back negative but your symptoms are strong, your doctor will usually follow up with an in-lab polysomnography to get a more complete picture.
How the AHI Determines Severity
The core diagnostic number is your AHI, which counts every apnea (complete breathing pause lasting at least 10 seconds) and hypopnea (partial airflow reduction with a drop in oxygen or a brief awakening) per hour of sleep. The severity scale is straightforward:
- Mild: 5 to 14 events per hour
- Moderate: 15 to 30 events per hour
- Severe: more than 30 events per hour
Fewer than 5 events per hour is considered normal. To put severe apnea in perspective, an AHI above 30 means your breathing is disrupted at least once every two minutes throughout the night.
Your sleep report will also include the oxygen desaturation index (ODI), which counts how many times per hour your blood oxygen drops by 3% or more for at least 10 seconds. The ODI closely tracks the AHI and adds important context. An ODI above 20 identifies severe sleep apnea with 97% sensitivity. Some clinicians use overnight pulse oximetry alone as an initial screen: if your ODI is below 15, severe sleep apnea is very unlikely, and if it’s above 20, further evaluation is strongly warranted.
Obstructive vs. Central Sleep Apnea
The sleep study doesn’t just count breathing events. It also identifies why they’re happening, which determines whether you have obstructive or central sleep apnea.
In obstructive sleep apnea, the airway physically collapses or narrows. The chest and belly sensors show that your body is still trying to breathe, the muscles are working, but air can’t get through. This is by far the more common type.
In central sleep apnea, the brain temporarily stops sending the signal to breathe. The chest and belly sensors show no respiratory effort at all during the pause. This distinction matters because the two types have different causes and different treatments. Central sleep apnea is more common in people with heart failure or those using certain medications, and it requires different management than the standard CPAP therapy used for obstructive cases.
Many people have a mix of both, called complex sleep apnea. The ratio of obstructive to central events in your study helps guide which treatment approach your doctor recommends.
What Happens After the Study
A board-certified sleep physician reviews your raw data and generates a report, usually within one to two weeks. The report includes your overall AHI, the breakdown by sleep position (apnea is often worse when sleeping on your back), oxygen levels throughout the night, and any other findings like periodic limb movements or abnormal heart rhythms.
If your AHI is 5 or above and you have symptoms, you’ll typically receive a diagnosis of obstructive sleep apnea. In some cases, particularly for moderate to severe results, your in-lab study may include a “split night” format: the first half is diagnostic, and once enough apnea events are recorded, the technologist wakes you, fits a CPAP mask, and spends the second half calibrating the air pressure to keep your airway open. This saves you from needing a separate night for treatment setup.
For mild cases, your doctor may discuss positional therapy, weight management, or an oral appliance before recommending CPAP. For moderate to severe cases, CPAP is the standard first-line treatment, and your study results will directly inform the pressure settings programmed into your machine.