The oximeter and the pulse oximeter has become one of those utensils whose existence many did not know until the COVID-19 pandemic. Now we all know what it is and, in addition, many people have one in their homes. The reason is that the decrease in oxygen saturation it has been considered one of the indicators of severity of the disease. But having it is not enough. You also have to know how to use it and, above all, take into account that certain factors can distort the results. For example, it has been found that in people with black or very brown skin are more likely to be obtained misleading results.
It has been known for a long time. In fact, in December 2020 it was already published A study about. In it, it was mentioned that the investigation of this phenomenon began in the early 2000s. But, even so, it is information that even many health professionals were unaware of.
For this reason, some health authorities they have echoed of the issue during the pandemic. First was the fda, shortly after the December study was published. Now, it has been the NHS From United Kingdom. In general, they all agree on the same thing. That this finding does not mean that black skinned people cannot use an oximeter. But they must take into account the errors that they could throw.
The importance of using an oximeter
During the coronavirus pandemic, a very relevant fact about this disease has been verified: that some people suffer a drastic decrease in the blood oxygen concentration, but without actually feeling like they are drowning. This silent symptom is a danger; since sometimes, by the time they realize it, the lungs are already too damaged.
Therefore, it is recommended that people with COVID-19 have an oximeter to check periodically this parameter. Even for people at risk, such as the elderly residing in social health centers, the recommendation was made to analyze their oxygen saturation frequently, without necessarily being infected.
This has led many people to buy one of these devices in the last year. A healthy result is considered to be between 95% and 100%. However, some lung diseases, such as COPD, they can yield much lower percentages without any added problem. Therefore, rather than an isolated result, the recommendation is that we look at the evolution of these figures. If we have tested positive for COVID-19 and we see that the oxygen saturation in various measurements with the oximeter is drastically decreasing, we should ask our doctor or, if the decrease is very pronounced, go to the emergency room. Especially if it goes below 90%.
This is applicable to the entire population, but with nuances for the black skinned people. They may have results that do not correspond to reality, due to an overestimation. However, the evolution of the percentage, erroneous or not, is still a indicative data very useful.
Why does it give wrong results in people with black skin?
When we take in air, the oxygen present in the lungs is distributed through the blood to all the tissues of the body. Those in charge of this transport are the Red blood cells, but they couldn’t do it without hemoglobin, a protein that is precisely responsible for capturing it.
It is possible to know if this protein is bound to oxygen or not because in each case it absorbs light in a different way. So what oximeters do is emit infrared radiation towards the skin. They can be placed in different places on the body, although the finger, because it receives a large blood flow through the capillaries.
The device has a sensor that measures how much of that light was emitted is absorbed. Thus, a calculation can be made of the amount of red blood cells that are carrying oxygen and, therefore, of the concentration that we have of this substance in the blood.
The problem is that, in the same way that a wall does not absorb the same light if it is white or if it is painted black, in this case, it has been seen that the light spray on the oximeter can also be affected by colors. For example, it is recommended not to use it on fingers with painted nails, as the results could be falsified. And the same happens if the user has the black skin.
In fact, in the December 2020 study, when making measurements at 10,000 patients, it was seen that those with white skin obtained a 3.6% misleading results, while in those with black skin the result rose to 11.7%. Possibly, if it had been tested on more black-skinned people at the time of its development we would have been aware of this matter much earlier. Very often scientific research is carried out mainly in men cis White skin. And that leaves the rest of the population out of the results. We have seen it with women and this is not the first issue that involves a prior ignorance of the effects in patients with black skin.
Therefore, the oximeter results on a black-skinned person may not be a reflection of reality. But if they are measured in successive days and a drop in the percentage is observed, that person should consult a health worker as soon as possible. Whatever the color of your skin.