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Pulse Oximetry

Interpreting Overnight Oximetry Readings

By Shirley · Updated November 2, 2026 · 3 min read
DisclosureSome links here are affiliate links — if you buy through one I earn a small commission at no extra cost to you. It does not affect which devices I recommend. A post a brand paid for, or one with a brand's paid link to its product, says so in its first line.
Please read this firstThis is general information, not medical advice, and nothing here is a diagnosis. Home health devices can be wrong — a fingertip oximeter can read falsely high or low depending on circulation, nail polish, movement and skin temperature. If you feel unwell, or a reading worries you, contact your doctor or emergency services rather than re-testing until you get a number you like.

For those of you with an overnight pulse oximeter you know that one of the highlights of these devices are the readings that get conveniently sent to your phone or computer.

The app or software organizes your overnight oximetry readings for you and creates tables and graphs all for you to share with your physician.

But what if you can’t wait for your next appointment with your physician?

In Need for a New Pulse Oximeter?

Let me tell you about the Wellue O2Ring – it’s like the superhero of pulse oximeters, seriously!

One of the coolest things about it is that it doesn’t just clip onto your finger like your average oximeter.

Wellue O2ring

Nope, it’s a smart ring that you wear on your finger, making it super comfortable and convenient.

You won’t even feel like you’re wearing anything special, yet it’s working its magic behind the scenes.

Check out their official product page here.

Overnight Oximetry Readings How?

Interpreting overnight oximetry readings yourself can be difficult if you’re not some sort of healthcare professional, so here I aim to help you better understand your results.

Referring to the image on the right, see my explanations below of each of the results provided by your overnight pulse oximeter.

Interpreting Overnight Oximetry Readings

  • Recording time: the length of time you used the pulse oximeter to collect readings.

    In other words, from the time you put it on and start it to the time you take it off.

  • <90% Time: the length of time your peripheral oxygen saturation (SpO2) dropped below 90%.

    A value of 90% is used here because drops in SpO2 below 90% are when you get into the moderate (80-89%) and severe (below 80%) oxygen desaturation ranges.

  • Drops over 4%: the number of times your SpO2 decreased by 4% or more. These drops are indicated as the small white triangles at the bottom of the SpO2 graph.

    Unless you changed the presets, these are the times when your pulse oximeter vibrated throughout the recording session to let you know your oxygen level dropped below normal range.

  • Drops per Hour: the average of the number of times your SpO2 decreased by 4% or more per hour throughout the recording session.

    Essentially, this could be seen as the average number of times you experience notable oxygen desaturation per hour.

    This number is your Oxygen Desaturation Index (ODI), often written ODI4 when it counts 4% drops. It is not your Apnea Hypopnea Index (AHI): the AHI counts the times an hour your breathing stopped or got shallow, and only a sleep test, which measures your airflow and breathing effort, can give it. The two often move together, so a high ODI is a good reason to ask your doctor about a sleep test.

  • Average SpO2: overall average of your SpO2 readings gathered throughout the recording session.

  • Lowest SpO2: the lowest SpO2 reading gathered throughout the recording session.

  • O2 Score: the overall assessment of oxygen shortage throughout the recording session. It is a combined assessment of frequency, depth, and duration of drops in oxygen saturation.

    This score ranges from 0-10, with a higher score meaning that the blood is the most saturated with oxygen (in other words, the higher your score on the range of 0-10, the better).

    The O2 Score correlated with the bar to the right of it that changes from red to yellow to green. Wellue states that if you fall in the yellow or red, you should notify your physician.

  • Average HR: overall average of your heart rate reading gathered throughout the recording session. Normal heart rate is generally between 60-100 beats per minute (bpm); most healthy adults have a resting heart rate of below 90 bpm.

My Final Words

The accuracy of pulse oximeters can vary from brand to brand and device to device. If you have the Wellue O2 Ring, I would say it’s as accurate as these devices can get.

If your SpO2 falls between 80-99%, SpO2 can be off by about +/- 2%. If your SpO2 falls between 70-79%, then SpO2 can be off by about +/- 3%.

Still looking to learn more about pulse oximetry?

Do you have sleep apnea and want to learn more about how pulse oximetry is used in sleep apnea? See my articles below:

Written by

Shirley

Shirley writes Self Health Pharmacist's guides to home health devices: pulse oximeters, CPAP machines, sleep trackers and hearing aids. Each guide explains what the reading actually measures, what a normal range looks like, which features are worth paying for, and the point at which a device stops being useful and you need a person instead.

A device is not a diagnosis. The guides tell you what a number means, and they say plainly when it means call your doctor.

A note on our names: Self Health Pharmacist is written by a small team under pen names, one name for each job, and Shirley is the name on our device guides. The site's name is its brand, not a job title: we are not pharmacists, and nothing here replaces your own pharmacist or doctor.

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