What Is AHI and How Do I Know If I Need CPAP Therapy?

By Yash, RRT — Licensed Respiratory Therapist & Owner, MyRespCo

If you’ve been told you have sleep apnea, or if you’ve just received a home sleep test report, you’ve probably seen the letters AHI and a number next to them. That number is one of the most important metrics in sleep medicine — and understanding it will help you make better decisions about your treatment.

What Does AHI Stand For?

AHI stands for Apnea-Hypopnea Index. It measures the average number of breathing disruptions per hour of sleep. It is the primary metric used to diagnose obstructive sleep apnea (OSA) and determine its severity.

There are two types of events counted in the AHI:

  • Apnea: A complete cessation of airflow lasting at least 10 seconds. During an apnea, you stop breathing entirely.
  • Hypopnea: A partial reduction in airflow (typically ≥30% reduction) lasting at least 10 seconds and associated with a drop in blood oxygen saturation or an arousal from sleep.

Both events count equally toward your AHI score.

AHI Severity Classification

  • AHI 0–4: Normal — no clinically significant sleep apnea
  • AHI 5–14: Mild OSA — CPAP therapy is often recommended depending on symptoms
  • AHI 15–29: Moderate OSA — CPAP therapy is strongly recommended
  • AHI 30+: Severe OSA — CPAP therapy is essential; untreated severe OSA carries significant cardiovascular and metabolic risk

What Does Your AHI Actually Feel Like?

An AHI of 30 means you are stopping or partially stopping breathing 30 times every hour — once every two minutes throughout the night. Most patients have no memory of these events. The brain arouses briefly to restore breathing, but not fully enough to wake you. The result is fragmented, non-restorative sleep even if you technically spent 8 hours in bed.

Common symptoms of untreated OSA include: waking unrefreshed regardless of sleep duration, excessive daytime sleepiness, morning headaches, difficulty concentrating, irritability, and in severe cases, falling asleep during passive activities like watching TV or riding in a car.

How Is AHI Measured?

AHI is measured during a sleep study, either in-lab (polysomnography) or at home (home sleep apnea test, HSAT). A home sleep test typically measures airflow, respiratory effort, blood oxygen saturation, and heart rate. The resulting data is interpreted by a sleep physician or qualified clinician to generate your AHI score and diagnosis.

What Happens After Diagnosis?

If your AHI is ≥5 with symptoms, or ≥15 regardless of symptoms, CPAP therapy is the first-line evidence-based treatment. CPAP (Continuous Positive Airway Pressure) works by delivering pressurized air through a mask to maintain airway patency throughout the night — eliminating apneas and hypopneas entirely when set correctly.

A CPAP machine with AutoSet functionality automatically identifies and delivers the optimal pressure for your anatomy — no manual titration required. At MyRespCo, our refurbished ResMed AirSense 10 AutoSet is the most popular starting machine for newly diagnosed patients.

What If My AHI Is Borderline (5–10)?

Borderline AHI requires clinical judgment. If your AHI is 5–10 but you have significant daytime symptoms, cardiovascular risk factors, or a physically demanding job (including CDL driving), treatment is often recommended. A $49.99 RT Consultation with our Licensed Respiratory Therapist is an efficient way to review your data and understand your options without navigating an insurance maze.

→ How to Get a CPAP Without a Prescription
→ Book an RT Consultation — $49.99
→ Shop Refurbished ResMed AirSense 10 AutoSet