ViHealth O2 Score: What It Means and What It Doesn't

You wake up, open ViHealth to see how the night went, and the first thing the app shows you is a single number with a colour behind it: your O2 Score. It is the most glanceable thing in the report and the least explained. A 9 feels reassuring, a 6 feels alarming, and almost nobody knows what separates them. Here is what the score actually measures, how much weight to put on it, and what it cannot tell you.

What the O2 Score is

The O2 Score is Wellue's summary of how much oxygen shortage your night contained. In the manufacturer's own ViHealth FAQ, it is defined as "a measure of oxygen shortage during whole sleep" that combines three things: how often your oxygen dropped, how long the drops lasted, and how deep they went. Higher is better — a higher score means oxygen stayed richer through the night, a lower one means it was short more often, for longer, or further down.

Why three nights with the same low reading can score differently

Because the score is built from frequency, duration and depth together, no single one of them decides it. A night with one deep but brief dip can score better than a night with many shallow ones that each lasted several minutes. This is why people are so often confused by the score moving while their lowest reading of the night stayed the same — the lowest number is one input of three, and it is not the most heavily weighted one. If you want to understand the events behind the score, the dips themselves are covered in why SpO₂ drops during sleep.

How to read the colour

ViHealth pairs the number with a colour that runs from red at the poor end to green at the good end, so you can read the night at a glance without interpreting the figure. Worth knowing: Wellue does not publish the exact cut-offs where one band becomes the next. That is a real limitation and it is the reason to treat the score as a relative indicator — useful for comparing your own nights against each other — rather than as a threshold you have passed or failed. A drop from 9 to 7 across a week of your own nights is meaningful information. A 7 in isolation is not a verdict.

What the O2 Score is not

• It is not a diagnosis. A low score is a prompt to pay attention and, if it persists, to talk to a doctor — it does not identify a condition or rule one out.
• It is not an AHI. Sleep apnoea is scored clinically by breathing events per hour, measured with equipment a ring does not have. The O2 Score measures oxygen, not breathing.
• It is not comparable across apps or devices. Other oximeters and apps compute their own overnight scores with their own formulas, so a 7 here does not equal a 7 elsewhere.
• It is not independent of signal quality. A poorly seated ring or cold hands produce artefacts that the score cannot distinguish from real desaturations.

That last point causes more bad nights of sleep-score anxiety than any other. If your reading looked erratic, check the perfusion index before you believe the score built on it — a weak signal makes every number above it less trustworthy, as explained in what PI (perfusion index) means.

Things that move the score without anything being wrong

Before reading much into a single bad night, rule out the ordinary explanations. A ring worn loosely or slipped down the finger, cold hands and poor circulation, alcohol in the evening, nasal congestion from a cold, sleeping flat on your back, or simply a night at altitude will all push oxygen readings down. Altitude in particular shifts the whole baseline — see blood oxygen at high altitude. One unusual score among a run of normal ones is usually noise. A pattern is what deserves attention.

What to do with a low score

Repeat it. A score is a sample of one night, and the useful signal is whether it recurs. Wear the ring properly across several nights, note anything unusual about each one, and look at the run rather than the outlier. If low scores persist — particularly alongside daytime sleepiness, morning headaches, loud snoring or witnessed pauses in breathing — that is worth a conversation with a doctor, and the recorded data is worth bringing with you. ViHealth can export the underlying reports, which are far more informative to a clinician than the summary number. If you want a more structured way to gather several nights, see the overnight pulse oximetry test guide, and for the sleep-apnoea context specifically, using a pulse oximeter for sleep apnoea.

The gap the score can't close

Here is the structural limit of any overnight score: it arrives in the morning. The O2 Score is calculated after the fact, from data the ring stored and synced to the phone beside it. That is fine when you are scoring your own sleep and reviewing it over coffee. It is the wrong tool if the person you are worried about is not you — because a score cannot wake anyone, and the night it describes is already finished. If what you actually want is to know while it is happening, that is a different job: OxyRemote reads the same Wellue ring over Bluetooth and streams the readings live to other people's phones, sending a push alert the moment oxygen crosses a threshold you chose. Families watching a parent or a partner usually keep ViHealth for its reports and scores, and add a live layer for the watching — the two are covered side by side in ViHealth vs OxyRemote.

The bottom line

The O2 Score compresses frequency, duration and depth of your overnight oxygen drops into one number, coloured red to green, where higher is better and 10 means no hypoxia was detected. Read it as a way of comparing your own nights, not as a grade — Wellue does not publish the band boundaries, and signal quality can move it on its own. Repeat a bad night before believing it, take a persistent pattern to a doctor with the exported data, and remember that a morning score and a live alert solve genuinely different problems.