Reportage. US research shows the tools used to measure blood oxygen work poorly on Blacks and Hispanics. Access to Covid treatment may have been altered. The disparity may have contributed to increased mortality in minorities.

In America, even the pulse oximeters are racist

In addition to violent cops and white supremacists, Black Americans also have to contend with seemingly harmless pulse oximeters. The devices, which became wildly popular during the pandemic, discriminate between ethnic minorities and white people when it comes to measuring blood oxygenation, making the blood of Black and Hispanic people appear richer in oxygen than it really is. And this, especially during the worst periods of the Covid emergency, has altered the assessment of the severity of patients and caused a disparity in care in people belonging to minorities.

Thus, the different impact of Covid-19 in the United States can be explained, at least in part: while life expectancy has dropped by about a year among white Americans, three years of life have been lost among Black and Hispanic Americans. This is suggested by a study published in the scientific Journal of the American Medical Association (Jama) of Internal Medicine by doctors at the university polyclinics of Maryland and Texas, led by Ashraf Fawzy of the Johns Hopkins University of Baltimore.

The problem of the “racist oximeter” has been known for over thirty years. During Covid-19, as in all lung diseases, it represented the most important tool for assessing the situation of a Covid-19 positive person. The 94% blood saturation threshold is normally used to distinguish a non-severe patient from one requiring more intense therapies, such as antiviral drugs and mechanical ventilation.

The most used models measure the amount of oxygen in the blood by transmitting a beam of light through a finger and detecting how far it can pass through it. Since hemoglobin influences the absorption of some frequencies of radiation, this optical and non-invasive measurement — just tighten a clip around the fingertip — allows you to evaluate the percentage of oxygen. However, the pigmentation of the skin also interferes with the light beam and can distort the result. On a sample of about 7,000 patients, the researchers showed that the oxygenation of Black, Hispanic and Asian patients is overestimated by 1-2% compared to the real values, while in white patients the instrument gives a lower value than the real one. The defect led to the judgment of not serious cases which required more intensive care.

The difference in percentage may appear small, but it becomes decisive in cases close to the fateful 94% threshold: the data shows that Black and Hispanic patients have a 29% and 23% lower probability, respectively, of receiving treatment appropriate to their state based on the oximeter results. The likelihood of hypoxia going undetected by doctors is nearly three times higher in these minorities than in whites.

Although the problem is not unpublished — the first study that highlighted the problem dates back to 1991 — these analyses are not well known among healthcare professionals. “This is not new information, but I can certainly say that I have not received any instructions on this,” Fawzy told StatNews magazine.

The malfunction of pulse oximeters is not an isolated case. Other diagnostic tools are also less accurate than used on Black patients. In the longest known cases, from spirometry to tests on the functioning of the kidneys, doctors today use correction coefficients to take into account ethnic differences.

But, as the case of pulse oximeters shows, this is not the rule. The disparities in health conditions, very evident in countries without a universal health service such as the United States, cannot in fact be explained only by the lack of access to health facilities for economic reasons or with less healthy lifestyles. One of the most extensive surveys on the subject carried out in 1997 in the US on 1.7 million patients and 77 different pathologies revealed that for the same age, severity, insurance coverage and type of hospital, for almost half of the diseases Black patients had a significantly smaller chance at receiving adequate therapies.

The fact that the ineffectiveness of health tools regularly affects the most vulnerable minorities is no coincidence. In fact, drugs and medical devices are placed on the market after a series of experiments on samples of volunteers who rarely reflect the real population, despite the frequent recommendations of regulatory agencies such as the Food and Drug Administration. People belonging to ethnic minorities participate more rarely in the trials: what counts is the fear of anti-ethical discrimination, based on a history of American medicine dotted with episodes of racism, but also the economic difficulty of accessing the most qualified health facilities in which these experiments take place. As a result, little is known about the effectiveness of drugs and devices on Black, Hispanic and other minority populations.

The result is particularly visible in the sector of respiratory diseases, which affect the black population with greater severity. A 2015 US research showed that only 1.9% of all clinical trials in this area included minority subjects. A similar fate concerns women, who are also much less represented than men in the trials. The consequence is that much of the medicine we have is designed for a white, male and well-to-do population, while the social groups that need it are left out.

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