Is my number normal?

What counts as low blood oxygen?

By GyroscopeUpdated November 14, 202611 sources

Awake and resting, under 95 is below normal, 92 or lower means call your doctor, and 88 or lower means get medical care now. Asleep, or sleeping somewhere high, your number runs lower than that, and it’s supposed to.

Why does low depend on when you measured?

The same number means different things at different moments, the way 45 miles an hour is fine on a highway and scary outside a school. A watch that shows 89 at 3 am and a finger clip that shows 89 while you sit at the kitchen table are telling you very different things.

The awake lines come from MedlinePlus, the US National Library of Medicine’s health site. The night range comes from 33,080 Apple Watch wearers, and the lowest point from 350 people whose sleep studies were normal.

Why do doctors draw the line at 92?

Healthy blood sits on a flat stretch near the top. Breathe a little less or go a little higher and the number barely moves, because nearly every oxygen seat stays filled. Lower down, the curve turns steep, and small changes in the oxygen reaching your lungs move the number a lot. Luks and Swenson, two doctors who study oxygen at altitude, write that up high, saturation changes fast with small changes in oxygen.

The researchers behind the big Apple Watch study write the same lines as MedlinePlus. Under 92 while breathing ordinary air at sea level usually gets a closer look, and values that stay under 90 point to low oxygen in the blood.

There’s a second reason to act at 92 instead of waiting. Sensors tend to show too high when oxygen is low. Below a true 88, a medical finger oximeter was off by about 3.5 points and an Apple Watch Series 7 by about 6, in 9 young adults breathing controlled low oxygen, and both leaned high. In hospital patients whose oximeter showed 92 to 96, the blood test found true oxygen under 88 for 11.7% of Black patients’ measurements and 3.6% of White patients’. A 92 on the screen can be lower in your blood.

What can throw the number off?

Cold hands, dark nail polish, fake nails, poor circulation and moving around all throw a finger oximeter off, MedlinePlus and the FDA say. A loose watch band, or some tattoos under the sensor, can do the same to an Apple Watch, Apple says. Darker skin and smoking are on the official lists too, and both tend to push the number up, so they can hide a low one. The fix for a surprising low number is a second try done right: sitting still, hand warm and below your heart, until the number stops changing (how to measure it).

Is low different if you live up high?

A little. MedlinePlus says levels can run lower if you live at a higher elevation, and in the watch study each kilometre (3,300 feet) of elevation took about 1.2 points off a typical night. Above about 8,200 feet the study’s straight line stops working, and the CDC says people with altitude sickness usually show a number that’s normal for the altitude. Up there, how you feel decides (what’s normal at altitude).

Children’s numbers differ, so ask your child’s doctor.