Pulse oximeters and other devices for monitoring aspects of our health may work better for some than others.
In recent years, there has been a veritable explosion in the number and types of health monitoring devices available in smartphones and fitness apps.
Your smartphone is potentially tracking the number of steps you take, how far and fast you walk, and how many stairs you climb each day. Some phones log sleep, heart rate, how much energy you’re burning, and even “health gait” (how often are both feet on the ground? How similar are your strides?). And, of course, there are non-phone wearables and fitness gadgets available, like devices to measure your heart rate, blood pressure or oxygen levels. The accuracy of these devices varies—and, in some cases, your skin tone can make a difference.
In general, how accurate are health monitors?
I know from my experience with hospital monitoring devices that they are not always accurate. False alarms from EKG monitors often send medical staff to the patient’s room, only to find the patient feeling fine and wondering about the commotion. A particularly common false alarm is an alarming and unstable heart rhythm on a continuous heart monitor, which may be caused by the motion of the patient brushing his teeth.
High-stakes devices with monitoring capabilities, such as defibrillators and pacemakers, are extensively tested by their manufacturers and scrutinized by the FDA, so their accuracy and reliability are generally quite good.
But what about home health monitoring devices intended for consumer use that haven’t been tested extensively by the FDA? Ever counted your steps for a few minutes just to see if your phone’s tally agrees? Or take a few stairs to see if you’re getting all the credit for not taking the elevator?
The accuracy of consumer devices depends in part on what is being monitored. For example, one study assessed the accuracy of heart rate monitors and energy expenditure calculators in phones and health apps. The accuracy was quite high for heart rate (often in the range of 95%), but much less accurate for energy expenditure. Accuracy may also vary depending on Who? is being monitored.
Device Bias: What It Is and Why It Happens
While no health gadget is perfect, some users find results more reliable than others. For example, if you’re applying nail polish, a pulse oximeter — a device that clips onto the fingertip to measure blood oxygen through the skin — may not work properly, because the polish interferes with the light sensor’s proper sensitivity. interferes with work. In that case, there’s a simple solution: remove the polish.
But in other cases, the solution isn’t simple. Increasingly, we are recognizing that some medical devices are less accurate based on a person’s skin colour, a phenomenon known as device bias.
- pulse oximeter. Although generally considered highly accurate and commonly trusted in health care settings, their accuracy is lower in people of color. This is because the device relies on light shining through the skin to detect blood colour, which varies with oxygen level. The amount of pigment in the skin can change the behavior of light as it travels through blood vessels, giving inaccurate results.
- Bilirubin measurement in newborns. Bilirubin is a breakdown product of red blood cells. Newborns are screened for high levels because it can cause permanent brain damage. If detected early, phototherapy (light treatment) can help the baby get rid of excess bilirubin, thereby preventing brain damage. Screening includes examining a newborn’s skin and eyes for jaundice (a yellowing condition caused by high bilirubin) and a light meter test to detect high bilirubin levels. But the accuracy of this test is lower in black newborns. This is especially important because jaundice is more difficult to detect in babies with darker skin, and dangerously high bilirubin levels are more common in this population.
- Heart rate monitor in smartphone. Smartphone apps may also be less accurate among people of color, according to at least one study. Again, this is because the more skin pigment present, the more difficult it is for the light sensors to detect the pulse in the bloodstream that represents the heartbeat.
Why device bias matters
Sometimes an error in measurement has no immediate health consequences. An error rate of 5% to 10% can be of little consequence when measuring heart rate. (Indeed, one might ask why does one need a device to monitor heart rate when you can simply count your pulse for 15 seconds and multiply by 4!)
But pulse oximeter readings are used to help decide whether a person needs hospitalization, who needs admission to an intensive care unit, and who needs additional testing. If people of color are consistently shown to have overestimated oxygen levels, they may be more likely to be treated than other people, who have more accurate readings. And it could make pre-existing health disparities worse.
These examples add to a growing list of implicit biases within healthcare, and other examples where failing to include diverse individuals has serious consequences. When you use a health tool, it’s fair to wonder whether it’s been tested on people like you. It is also reasonable to expect people developing medical and consumer health devices to detail the demographics of test subjects to ensure results are reliable for all users before putting them on the market.
Sometimes a change in technology, such as using a different type of light sensor, can make healthcare devices work more accurately for a wider range of people.
Or there may not be an easy fix, and user characteristics will need to be factored into proper interpretation of the results. For example, a device may provide the user with a skin color option to match the skin tone. Then based on extensive data from prior testing of people with different skin colors, the device can adjust the results appropriately.
Bottom-line
The push to keep track of our bodies, our health, and our life experiences continues to gain momentum. That’s why we need to thoroughly test and validate healthcare devices to ensure they work for a variety of individuals before declaring them suitable for the general public. An FDA expert panel has advocated for better regulation and testing of pulse oximeters to ensure they are accurate for everyone.
Even with the best testing, device bias can’t disappear: bodies differ, and technology has its limits. The key is to recognize that it exists, fix what can be fixed, and interpret the results accordingly.
Follow me on Twitter @RobShmerling
