Overnight Oximetry: What Your ODI and SpO2 Mean

Type the numbers your O2Ring, Lookee, wrist oximeter or sleep-clinic report gave you. Each one is read back with what is actually published about it — and with what this kind of recording cannot tell you.

One night, as a wrist or finger device recorded it

Your report, read line by lineEvery one of these numbers is a screening figure from a device on your finger or wrist.

The bands people quote — and where they actually come from
Events per hour	What that band is called on a SLEEP STUDY

This page explains numbers a device produced; it does not diagnose anything and it cannot rule anything out. Overnight oximetry does not measure breathing, effort or sleep itself — if you snore heavily, stop breathing in your sleep, or are tired every day, ask your doctor for a proper sleep study.

Definitions and sources checked 2026-09-22.

Quick answer: a consumer overnight oximetry report has four numbers that matter — the average, the lowest reading, the ODI (how many times an hour your oxygen dipped) and the time below 90%. There is no published severity scale for any of them from a ring or a wrist device: the “mild / moderate / severe” bands you will find quoted belong to the apnoea–hypopnoea index, which comes from a full sleep study, not from an oximeter. What is published, and what this page gives you, is what each number means, what healthy sleepers actually record, and the ODI cut-offs that predicted a sleep study’s result in two published studies.

How to use it

Type the numbers your app shows. The one setting that matters is whether your device counts 3% or 4% dips — the same night scored at 3% always gives a bigger ODI, so a number without its threshold cannot be compared with anything. Most apps show it in their settings; the O2Ring and similar devices let you choose.

What each number is worth

Average SpO₂

The least useful of the four on its own. A night can average 95% and still contain a hundred dips, because an average flattens exactly the pattern that matters. It becomes important when it is low, because a steadily low average points at something continuous rather than at pauses in breathing.

The lowest reading (nadir)

Healthy sleepers dip, and further than most people expect. In 330 people whose overnight sleep studies came back normal, the average lowest reading of the night was 90.4%, with most between 84.2% and 96.6% — and for people over 60, an average nadir of 89.3%. One dip is not a finding. A finger slipping out of a clip also produces one.

The ODI

The number of times per hour your oxygen fell by at least 3% or 4%. This is the number a clinician looks at first, because a repeated pattern of dips is what breathing pauses look like from the outside. In a study comparing home oximetry with respiratory polygraphy, an ODI at 4% of 5.4 an hour or more caught everyone who turned out to have an AHI of 10 or more, and 10.5 an hour or more everyone with an AHI of 30 or more, both with specificity above 85%. A separate JCSM study found ODI ≥ 10 was 95.65% sensitive and 81.48% specific for an AHI of 15 or more.

Time below 90%

How long the oxygen was low, rather than how far it fell once — which is why it is the number to take seriously. Medicare’s own criterion for covering home oxygen is a saturation of 88% or below during sleep, on a properly ordered test of at least two hours.

What this recording cannot tell you

Overnight oximetry records oxygen and pulse. It does not record airflow, breathing effort, body position, brain activity or arousals — so it cannot tell an obstructive event from a central one, cannot produce an AHI, and a normal-looking night does not rule sleep apnoea out. Its published job is to help decide who needs a proper sleep study first.

⚠️ One detail worth the date on this page: many sites still quote Medicare’s “for at least five minutes” wording for nocturnal oximetry. That wording was removed from the local coverage determination in its 1 January 2023 revision. Numbers in this area move, and a page without a checked date is not telling you when it last looked.

Worked examples

Average 94%, lowest 84%, ODI 12 at 4%, 3.2% of the night below 90%. The lowest reading is at the bottom edge of what healthy sleepers record; the ODI is above both published cut-offs, which is a reason to ask for a sleep study — not a diagnosis of anything.

ODI 12 at 3% dips. Not comparable with the cut-offs above, which were measured at 4%. If your device can report ODI4 as well, use that number.

A 90-minute recording. Too short to read. Medicare will not accept sleep oximetry under two hours, and a partial night catches whichever part of the night it caught.

FAQ

What is a normal ODI?

There is no published normal for the ODI a consumer device reports. What is published is what the ODI predicted about a sleep study: at 4% dips, 5.4 an hour or more caught everyone with an AHI of 10 or more, and 10.5 or more everyone with an AHI of 30 or more. Those are reasons to be tested, not gradings of your night.

What is a normal lowest oxygen level during sleep?

In 330 people with normal sleep studies, the average lowest reading of the night was 90.4%, with most between 84.2% and 96.6%; over the age of 60 the average nadir was 89.3%. Healthy sleep contains dips.

Is ODI the same as AHI?

No. The AHI counts breathing events on a full sleep study; the ODI counts oxygen dips on an oximeter. They correlate, which is why oximetry is used for screening, but the mild/moderate/severe bands belong to the AHI and are not published for the ODI.

Should my device count 3% or 4% dips?

Whichever it does, know which. The published cut-offs on this page were measured at 4%. The same night scored at 3% gives a larger number, so mixing the two produces a comparison that means nothing.

My oxygen dropped to 85% — is that dangerous?

A single reading cannot answer that, and this page will not pretend otherwise. Healthy sleepers reach the mid-eighties briefly. What a clinician looks at is how often and for how long, plus how you feel in the day — take the whole report to your doctor rather than one number from it.

Can overnight oximetry rule out sleep apnoea?

No. It measures oxygen, not breathing, and mild disease in particular can pass unnoticed. A normal trace with heavy snoring, witnessed pauses or daytime sleepiness still warrants a sleep study.

Does a low reading qualify me for home oxygen?

Not from a device you bought yourself. Medicare’s criterion is 88% or below during sleep on a test that was properly ordered and at least two hours long — the test has to be arranged by a clinician.

Overnight Oximetry Report Reader