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Oximetry results explainer

Overnight oximetry reports are a page of numbers with no sentences attached. Whether yours came from a clinic, a home sleep test, a ring, a watch, or the app that came with a finger oximeter, type in what it shows and get each figure placed against the reference ranges sleep clinics use, in plain English. Nothing you enter is sent anywhere.

Enter whatever your report gives you

Leave anything it does not show blank. Each figure is interpreted on its own, and the overall message comes from the most concerning one.

Called ODI, oxygen desaturation index, or sometimes "drops per hour". Choose 3% or 4% to match the report.

Also called the nadir or minimum SpO2.

The mean across the whole recording.

Often written T90 or "time under 90%". If the report gives minutes, divide by the length of the night in minutes.

Optional context. It never changes the overall verdict on its own.

Optional. Indices from under 4 hours of sleep are unreliable, and this will say so.

Where to find the numbers

Most reports lead with a desaturation index, written ODI, ODI3, ODI4 or “drops per hour”. Wellue’s ViHealth app shows it as “O2 drops” alongside a count of drops of 4% or more. Lowest SpO2 is usually labelled minimum, nadir or lowest. Time below 90% is sometimes given as a percentage and sometimes as minutes; if it is minutes, divide by the length of the recording in minutes to get the percentage this page wants. A clinic report will also carry an AHI, which no oximeter can produce and which this page does not interpret.

Why the bands are what they are

Desaturation index
The bands at 5, 15 and 30 events an hour are borrowed from the way sleep medicine grades the apnea-hypopnea index, because the two track each other closely in obstructive apnea. They are not identical: some events do not drop oxygen enough to count, so an ODI tends to run a little under the AHI of the same night.
Lowest SpO2
The oxygen dissociation curve is flat above 90% and steep below it, which is why 90 is the line. A nadir in the 80s says an event went deep; how much that matters depends on how often it happened, which is the index’s job.
Average SpO2 and time below 90%
These two describe the background rather than the events. A high index with a normal average and little time under 90% is many short dips, the classic obstructive picture. A low average with a high time under 90% and a modest index is sustained low oxygen, which points somewhere else, typically the lungs, and is a different conversation to have with a doctor.
Average pulse
Context only. It never changes the overall verdict, because a raised sleeping heart rate has too many innocent causes to count as evidence of anything on its own. It is worth a look alongside the rest.

If you have the recording, not just the report

The numbers are the summary; the trace is the evidence. Our free session viewer reads a Wellue CSV export or pulls a night straight off the device, charts it, and produces every figure above plus the ones most apps leave out, such as the length of the longest event and whether your heart rate shows the cyclical pattern that goes with obstructive events. It also prints to one page for an appointment. The blog goes into what ODI is and why it is the number to watch.