Pulse oximeters may be less accurate for black people. Do you need one?

Home pulse oximeters have been the personal technical gadget of 2020 and a reassuring way for patients to monitor their health at home under Covid-19.

But a new study showed that even in hospitals, pulse oximetry devices can sometimes be inaccurate, especially in black patients. The finding has raised questions about whether people with darker skin should rely on home surveillance.

Doctors say the devices that measure oxygen levels in the blood are still extremely useful in spotting declining health in all Covid-19 patients, including those with darker skin, before they become seriously ill. When the device is incorrect, the reading is probably only turned off by a few percentage points. What is important is that all patients, especially those with darker skin, are aware of any downward trend in oxygen readings rather than fixing a certain number.

“I think having information from a pulse oximeter is better than not having any information,” said Dr. Michael W. Sjoding, an assistant professor of internal medicine at the University of Michigan Medical School and lead author of the new report that appeared in the New England Journal of Medicine. “I would also say that you have to understand that a pulse oximeter is an imperfect device.”

A pulse oximeter looks like a chip clip. When you insert your finger into a pulse oximeter, it radiates different wavelengths of light through your skin. The amount of light absorbed reflects how much oxygen is in your blood. It has long been known that dark nail polish, cold skin and darker skin pigment can throw off the reading. However, the new study suggests that the problem occurs in black patients more often than most doctors thought.

The analysis, which was based on 1,333 white patients and 276 black patients admitted to the University of Michigan earlier this year, used a hospital-based pulse oximeter and compared it to the gold standard test for measuring oxygen saturation, called an arterial blood gas. sample. The study showed that pulse oximetry overestimated oxygen levels 3.6 percent of the time in white patients, but got it wrong almost 12 percent of the time in black patients. Normally, the pulse oximetry reading was overestimated by a few percentage points.

Researchers suspect that the inaccurate measurements may occur due to the way light is absorbed by darker skin pigments.

A normal reading on a pulse oximeter typically ranges from 96 to 100. Since patients with Covid-19 can calmly develop low oxygen levels without realizing it, patients are advised to monitor their oxygen levels at home. If the oxygen reading drops to 93 or 92, patients are advised to check in with their doctor. However, if a pulse oximeter sometimes overestimates the oxygen saturation level suggested by the Michigan study, the concern is that a dark-skinned patient who monitors himself at home may delay care if the monitor reads 94 or 95 incorrectly when the patient’s actual oxygen level may be 92 or 93.

The solution, said Dr. Sjoding, is that patients know their baseline reading on the home appliance and are aware of downward trends. If you are sick at home with Covid-19 and your normal reading drops by four points or more, this is a good reason to call your doctor.

While it is important to seek care, you do not need to panic. An oxygen saturation level in the low 90s is a concern for people with Covid-19, but it can be treated with supportive oxygen and placed on your stomach to increase oxygen flow to the lungs and possibly other treatments.

“I would say that if you happen to have a pulse oximeter at home, make sure you know what your normal level is so you can know what a change is for you,” said Dr. Sjoding. “If your home pulse oximeter read 98 when you bought it and you were healthy and now you’re 94 and you feel unwell, it’s a pretty strong sign that you’re sick and you should be seen by a doctor . ”

While the study focused on a group of patients who self-reported as African American, it is reasonable to believe that the risk of failure would be similar in other patients with darker skin color. The results are particularly worrying given that the pandemic is taking a disproportionate toll on black and Hispanic Americans, and studies have shown that African Americans have been hospitalized at a higher level, suggesting delays in access to medical care.

While the new data on pulse oximeter accuracy are important in helping physicians better interpret oxygen measurements in stained patients, Dr. Sjoding that the results should not scare consumers away from using the devices at home as long as they are aware of the limits. of the information provided by a pulse oximeter.

“My study is more about the emergency department physician having to make a decision about whether a patient should be admitted to the hospital or move a patient for intensive care,” said Dr. Sjoding. “For people at home, the pulse oximeter is still a device worth having, and there is still information that is valuable.”

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