Sleep Apnea: AHI vs RDI (How these measurements differ)
- Wellfirst Sleep
- Apr 27
- 3 min read
When you’re first handed your sleep study results, the jumble of acronyms can feel overwhelming. But two numbers—AHI and RDI—hold the key to understanding your sleep apnea diagnosis and crafting the right treatment plan. Let’s break down what they mean, why they matter, and how they can help you finally get the rest you deserve.
The Basics: What Are AHI and RDI?
Think of your sleep as a nightly journey. Along the way, your breathing might hit a few speed bumps—or even roadblocks. That’s where AHI and RDI come in.
AHI (Apnea-Hypopnea Index): This measures how many times per hour your breathing completely (apnea) or partially (hypopnea) stops while you sleep. It’s the go-to number for diagnosing obstructive sleep apnea and gauging its severity.
RDI (Respiratory Disturbance Index): RDI goes a step further. It counts all the apneas and hypopneas plus any other breathing disruptions that jolt you awake, known as RERAs (Respiratory Effort-Related Arousals). In other words, RDI gives a broader view of what’s really disturbing your sleep—even if you don’t technically “stop breathing”.
Why Both Numbers Matter
You might have a normal AHI but still feel exhausted, foggy, or irritable. That’s where RDI comes in. If your RDI is high, it means you’re experiencing subtle breathing interruptions that don’t meet the strict definition of apnea or hypopnea, but still ruin your sleep quality.
The RDI measurement also includes certain respiratory events named RERAs.
What is a RERA?
RERA stands for Respiratory Effort-Related Arousal. RERAs are important because they’re included in the Respiratory Disturbance Index (RDI), but not in the Apnea-Hypopnea Index (AHI).
While AHI only counts apneas and hypopneas, RDI gives a fuller picture by including RERAs as well. This means RDI is always equal to or greater than AHI, since it accounts for all AHI events plus these subtle but sleep-disrupting RERAs.
It’s when your breathing becomes abnormally shallow or restricted during sleep—but not enough to be called an apnea (pause) or hypopnea (partial blockage).
Even though it doesn’t meet the criteria for those, it still causes your brain to briefly wake up (an arousal).
You might not even realize it, but these small disturbances can mess with your sleep quality.
“RDI is particularly useful when symptoms of sleep apnea persist despite a normal or low AHI, highlighting that even small disruptions in breathing can significantly impact overall sleep quality,” explains Dr. Jack Maxwell, Sleep Specialist at Wellfirst Sleep.
Severity Levels at a Glance
Severity | AHI (events/hr) | RDI (events/hr) |
None/Minimal | < 5 | < 5–10 |
Mild | 5–14 | 5–14+ |
Moderate | 15–29 | 15–29+ |
Severe | 30+ | 30+ |
Note: RDI is always equal to or greater than AHI, since it includes all AHI events plus RERAs.
How Are These Numbers Calculated?
It’s all about the averages.
AHI: Add up all your apneas and hypopneas, then divide by the number of hours you slept.
RDI: Add apneas, hypopneas, and RERAs, then divide by hours slept.
For example, if you had 50 apneas, 75 hypopneas, and 20 RERAs during 6 hours of sleep, your AHI would be (50 + 75) ÷ 6 = 20.8. Your RDI would be (50 + 75 + 20) ÷ 6 = 24.2.
You can learn more about it here.
Why Does This Matter for Your Treatment?
AHI is the standard for diagnosing and grading sleep apnea, especially when considering treatments like CPAP therapy. But if your AHI is low and you still feel lousy, your RDI might reveal hidden sleep disruptions. This is especially important for people with upper airway resistance syndrome or unexplained daytime sleepiness.
“At Wellfirst Sleep, we look at the full picture—AHI, RDI, and your symptoms—to create a treatment plan that actually works for you,” says Gerard Jacob, CEO of Wellfirst Sleep.
What Should You Do With Your Results?
Once you have your sleep study results in hand, don’t just focus on one number. Talk with our sleep professionals about both AHI and RDI:
What do my AHI and RDI scores mean for my sleep quality?
If my AHI is normal but my RDI is high, what are my options?
How can we tailor my treatment to address all my sleep disruptions?
Taking the Next Step
Understanding your sleep study is just the beginning. At Wellfirst Sleep, we specialize in translating those numbers into real-world solutions—so you can reclaim restful nights and energized days. Whether your AHI or RDI is high, our team is here to guide you toward lasting relief.
If you’re ready for answers, clarity, and a custom plan that actually works, schedule your appointment with Wellfirst Sleep today. Let’s turn those confusing numbers into a clear path to Better Sleep, Better Health.
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