AHI vs RDI: Why Your Sleep Study Said "Normal" But You're Not

My sleep study came back "MILD OBSTRUCTIVE SLEEP APNOEA."

NHS said not significant enough for treatment. I felt dismissed. Again.

Years of exhaustion. Finally got a sleep study. And... nothing.

But I kept digging. Learned about AHI vs. RDI. That's where UARS was hiding.

I'm writing this between Christmas and New Year's. That strange week where time feels suspended. The world is quiet. If you're chronically ill, you know this feeling—the relief of no one expecting anything from you, mixed with the grief of another year struggling. This post is for those of us using these dark, still days to finally understand what's wrong.

What Is AHI?

Apnoea-Hypopnoea Index (AHI) — the number most doctors look at. It's the average number of apnoeas and hypopnoeas per hour of sleep.

What counts:

• Apnoeas: airflow drops by at least 90% for at least 10 seconds. Breathing essentially stops.
• Hypopnoeas: airflow drops by at least 30% for at least 10 seconds, plus a consequence—and here's where it gets messy.

The hypopnoea small print matters. The AASM scoring manual has two different rules a lab can use:

• The recommended rule: a 30% airflow drop counts if it comes with a 3% oxygen desaturation or an arousal (a brief brain-wave awakening).
• The acceptable alternative: a 30% airflow drop only counts if it comes with a 4% oxygen desaturation. Arousals don't count at all under this rule.

Same night of sleep, two different AHI scores, depending on which rule the lab used. If your breathing events wake your brain up without dropping your oxygen much—which is exactly what happens in UARS—the second rule can erase them from your score entirely.

Severity scale (these thresholds apply to AHI):

• Normal: fewer than 5 events/hour
• Mild OSA: 5–15/hour
• Moderate OSA: 15–30/hour
• Severe OSA: more than 30/hour

My AHI was just high enough for a "mild OSA" diagnosis. NHS said: not significant, no treatment offered.

But I was collapsing. Couldn't function.

What Is RDI?

Respiratory Disturbance Index (RDI) — the number that finally explained me.

RDI = AHI + RERAs, per hour of sleep. It counts everything in the AHI plus respiratory effort-related arousals.

What's a RERA?

A sequence of breaths lasting at least 10 seconds where you're working harder and harder to breathe—or the airflow signal flattens out—ending in an arousal from sleep. It doesn't meet the criteria for an apnoea or a hypopnoea, so it never touches your AHI.

Crucially:

• No full stop in breathing (not an apnoea)
• Usually no significant oxygen drop (not a hypopnoea, at least not under the stricter rule)
• BUT: it fragments your sleep, over and over, all night

This is the UARS pattern. And RERA scoring is optional—many sleep labs don't score them at all. They report AHI and stop there.

Why I Was Dismissed

First sleep study: my AHI qualified me for "mild OSA." But NHS wouldn't treat it.

I researched. Found RDI. Got a detailed analysis of my data.

My RDI was HIGH.

Dozens of RERAs per hour. My sleep was fragmented all night. But the report the doctors read had only led with AHI.

That gap between my AHI and my RDI is what UARS looked like on paper for me. That's why I felt terrible despite a "mild" label.

The Pattern

I hear versions of my story from so many people with UARS:

"My sleep study was normal." "They said I have mild OSA, not significant." "Doctor says I'm fine, but I feel terrible."

If that's you, it's worth asking whether your study only reported AHI—and whether anyone ever looked at RERAs or RDI at all. A low AHI with severe symptoms is exactly the situation where UARS hides.

What to Ask Your Doctor

Don't just accept "normal" or "mild" without understanding what was measured. These are the questions I wish I'd asked years earlier:

About the numbers:

• "What's my RDI, not just my AHI?"
• "Were RERAs scored on my study? If not, could the raw data be re-scored?"
• "Which hypopnoea definition did this lab use—the 3% desaturation-or-arousal rule, or the 4% desaturation rule?" (The answer changes the score.)
• "Could Upper Airway Resistance Syndrome explain my symptoms?"

About the test itself:

• Was it a home test or an in-lab polysomnography? Home tests don't record brain waves (EEG), so they can't detect arousals—which means they can't score RERAs, and they tend to underestimate how disturbed your sleep really is. If UARS is a possibility, that matters enormously.
• Is oesophageal pressure monitoring available anywhere? It's the classic gold-standard way UARS was identified in the research, though very few centres offer it.

Interpreting results:

• Low AHI + high RDI + severe symptoms is the combination worth raising with a sleep specialist.
• Ask for the detailed breakdown, not just "normal/mild/moderate."

If Your Doctor Dismisses You

This is the part that makes me rage. The medical gaslighting.

I was told, in effect: your AHI is barely mild, that's fine, you're fine.

No. I wasn't fine. My RDI told a completely different story—dozens of breathing-related arousals every hour. I was never reaching deep, restorative sleep.

What helped me:

• Asking specifically about RDI, in those words.
• Seeking a second opinion from a sleep specialist who knew UARS.
• Considering private testing when NHS wouldn't go further (I know—expensive, unfair).
• Bringing printed research to appointments.
• UARS communities (Reddit r/UARS, Hope2Sleep Facebook group) for support and resources.

You're not making it up. The data may already exist in your study. It's a question of whether anyone counted the right things.

The New Year's Reflection

It's December 27th. That weird liminal space between Christmas and New Year's.

For those of us chronically ill, this time of year is heavy. Another year gone. Still struggling. Watching everyone post their "New Year, New You" goals while you're just trying to survive January.

But here's what I'm learning:

These dark days—the shortest days of the year, the quiet between celebrations—they're not all bad.

There's less pressure. Less noise. The world slows down and for once, our pace doesn't feel wrong.

There's space for hard truths. Like: My sleep study said "mild" but I'm not mild-ly suffering. I'm severely impaired. And it took years to find a doctor who would look at the right numbers.

If you're using these quiet days to research, to understand your body, to prepare to advocate harder in the new year—that's not dramatic. That's survival.

We deserve doctors who look at ALL the data. Who don't stop at AHI. Who understand that "mild" on paper can be devastating in reality.

You Deserve Answers

If your sleep study said "normal" or "mild" but you're suffering, don't stop asking questions.

Ask about RDI. Ask about RERAs. Ask which hypopnoea rule was used. Ask whether anyone considered UARS.

You're not making it up. UARS is real. The exhaustion is real. The impact on your life is real.

Keep pushing. You'll find someone who listens.

Start here if you're newly diagnosed: What is UARS?

Understand why treatment isn't always enough: The CPTSD-UARS Connection

Note: I'm not a doctor. This is my personal experience. Consult healthcare providers for your situation.

Sources and review

I reviewed this post on 19 August 2026 and checked every definition against the sources below—because if I'm asking you to question your sleep study, I'd better get the small print right.

• The AASM Manual for the Scoring of Sleep and Associated Events, American Academy of Sleep Medicine (apnoea, hypopnoea, and RERA scoring rules, including the two hypopnoea criteria)
• StatPearls, "Apnea Hypopnea Index" (definitions and severity thresholds)
• Guilleminault et al., Chest, 1993 (the original description of upper airway resistance syndrome, using oesophageal pressure monitoring)
• Bao & Guilleminault, 2004 (UARS a decade on)

Everything about my own study—the low AHI, the high RDI, the years of being dismissed—is my personal experience, not medical advice.