When to get help

Does smoking affect pulse oximeter readings?

By GyroscopeUpdated November 14, 20266 sources

A little, and in the wrong direction. Smoke puts carbon monoxide in your blood, which a regular pulse oximeter can’t measure, and it can make your oxygen look higher than it is. In everyday smokers the error looks small. In carbon monoxide poisoning it can hide real danger.

How does carbon monoxide fool the sensor?

Carbon monoxide sticks to the same red blood cells that carry oxygen. A regular pulse oximeter can’t measure the carbon monoxide that’s on them, writes Neil Hampson, a doctor who has studied carbon monoxide poisoning at a hyperbaric treatment center. Special pulse CO-oximeters can estimate it, and a lab test on a blood sample measures it best.

How much is normal? Hampson puts nonsmokers usually under 2% and smokers usually under 5%. Above 9% almost always means carbon monoxide from somewhere else, even in a smoker.

The surprising part came in 1998, when Hampson looked at 30 people treated for severe carbon monoxide poisoning, every one with more than 25% of their blood carrying it. Their pulse oximeters showed oxygen consistently higher than the blood test found, and the gap grew as the carbon monoxide rose. The error was usually smaller than the carbon monoxide level itself, but the screens still showed more oxygen than the patients had.

Carbon monoxide is like a fake bill that gets past a quick glance at the register. A blood test is the bank that catches it.

How big is the error in everyday smokers?

Small, from the best numbers we’ve found. A 2022 study in Nottingham, England, paired 5,503 oximeter values with arterial blood tests, taken within 30 minutes of each other, in 3,266 hospital patients with COVID. At first, oximeters seemed to show smokers about 0.7 points too high. But the smokers also had lower true oxygen, and oximeters miss more at low oxygen. Once the researchers allowed for that, the extra error from smoking itself was close to zero. They found the big errors were below 90, smoker or not.

Is smoking on the official lists?

Yes. MedlinePlus lists tobacco use among the things that can throw off a pulse oximeter, the FDA lists current tobacco use, and so does the American Lung Association, alongside cold skin, nail polish and darker skin.

What about vaping?

We haven’t seen a study of vaping and pulse oximeter accuracy.

When should you get help?

If you think you’ve breathed carbon monoxide, get medical care whatever the oximeter shows, because only a blood test can measure it. And for anyone, smoker or not, trouble breathing, chest pain, new confusion, or gray or blue lips means calling 911 (when to go to the ER).