Home pulse oximeters have been the personal technology gadget of 2020 and a reassuring way for patients to monitor their health at home during Covid-19.
But a new study found that even in a hospital setting, pulse oximetry devices can sometimes be inaccurate, especially in black patients. The finding raised questions about whether people with darker skin should trust home monitoring.
Doctors say the devices, which measure blood oxygen levels, are still extremely useful for detecting declining health in all Covid-19 patients, including those with darker skin, before they become seriously ill. When the device is wrong, the reading is probably wrong by just a few percentage points. What is important is that all patients, especially those with darker skin, pay attention to any tendency to drop in oxygen readings, instead of settling on a specific number.
“I think having information from a pulse oximeter is better than having no information at all,” said Dr. Michael W. Sjoding, assistant professor of internal medicine at the University of Michigan School of Medicine and lead author of the new report, published in The new English medical journal. “I would also say that you must recognize 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 the skin. The amount of light that is absorbed is a reflection of how much oxygen is in the blood. It has long been known that dark nail polish, cold skin and darker skin pigment can impair 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 hospitalized at the University of Michigan earlier this year, used a hospital pulse oximeter and compared it to the gold standard test to measure oxygen saturation, called arterial blood gas test . The study found that pulse oximetry overestimated oxygen levels 3.6 percent of the time in white patients, but was almost 12 percent wrong in black patients. Normally, the pulse oximetry reading was exaggerated by a few percentage points.
The researchers suspect that inaccurate readings may be occurring 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 develop low oxygen levels silently 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 see a doctor. But if, as the Michigan study suggested, a pulse oximeter sometimes overestimates the level of oxygen saturation, the concern is that a dark-skinned patient who is self-monitoring at home may delay care if the monitor reads incorrectly 94 or 95, when the patient’s actual oxygen level can be 92 or 93.
The solution, said Sjoding, is for patients to know their baseline reading on the home device and pay attention to 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 need not panic. An oxygen saturation level in the 90s is a concern for people with Covid-19, but it can be treated with supportive oxygen, placed in the stomach to increase the flow of oxygen to the lungs and possibly other therapies.
“I would say that if you have a pulse oximeter at home, make sure you know what your normal level is so that you can know what a change is for you,” said Dr. Sjoding. “If your home pulse oximeter was 98 when you bought it and you were healthy, and now you are 94 and feeling bad, this is a strong sign that you are sick and should be examined by a medical professional. “
Although the study focused on a group of patients who called themselves African Americans, it is reasonable to think that the risk of error would be similar in other patients with darker skin. The findings are of particular concern, as the pandemic is disproportionately affecting blacks and Hispanic Americans, and studies have found that African Americans have been hospitalized at higher rates, suggesting delays in accessing medical care.
While the new data on the accuracy of the pulse oximeter is important in helping physicians better interpret oxygen readings in black patients, Dr. Sjoding noted that the findings should not scare consumers away from using the devices at home, provided they are aware of the limits of the information provided by a pulse oximeter.
“My study is more about the emergency department doctor who needs to make a decision on whether to admit a patient to the hospital or move a patient to intensive care,” said Dr. Sjoding. “For people at home, the pulse oximeter is still a device worth having and there is still valuable information.”
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