Analysis of 10,789 paired test results from 1,333 white patients and 276 black patients hospitalized at the University of Michigan earlier this year found that pulse oximetry overestimated oxygen levels in white patients 3.6 percent of the time, in nearly However, the time was 12 percent wrong or more than three times more likely in black patients.
In these patients, the pulse oximeter readings incorrectly indicated that the oxygen saturation level was between 92 and 96 percent, when in fact it was only 88 percent (results were adjusted for age, gender, and cardiovascular disease).
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- antibody: A protein produced by the immune system that can recognize and attach to certain types of viruses, bacteria or other invaders.
- Antibody test / serology test: A test that detects antibodies specific to the coronavirus. About a week after the coronavirus infects the body, antibodies start appearing in the blood. Because antibodies take so long to develop, an antibody test cannot reliably diagnose an ongoing infection. However, it can identify people who have been exposed to the coronavirus in the past.
- Antigen test: This test detects parts of coronavirus proteins called antigens. Antigen tests are quick and only take five minutes. However, they are less accurate than tests that detect genetic material from the virus.
- Coronavirus: Any virus that belongs to the Orthocoronavirinae virus family. The coronavirus that causes Covid-19 is known as SARS-CoV-2.
- Covid19: The disease caused by the new coronavirus. The name stands for Coronavirus Disease 2019.
- Isolation and quarantine: Isolation is separating people who know they have a contagious disease from those who are not sick. Quarantine refers to restricting the movement of people who have been exposed to a virus.
- Nasopharyngeal smear: A long, flexible rod with a soft swab that is inserted deep into the nose to collect samples from the space where the nasal cavity meets the throat. Samples for coronavirus tests can also be obtained with swabs that do not go as deep into the nose – sometimes called nasal swabs – or with mouth or throat swabs.
- Polymerase chain reaction (PCR): Scientists use PCR to make millions of copies of genetic material in a sample. With the help of PCR tests, researchers can detect the coronavirus even when it is scarce.
- Viral load: The amount of virus in a person’s body. In people infected with the coronavirus, viral loads can peak before symptoms, if any.
Oxygen levels below 95 percent are considered abnormal. “A small difference in pulse oximetry in this range of 92 to 96 percent could be the difference in deciding whether the patient is really sick or not, or whether or not they need other treatment. Said Dr. Sjoding.
Another analysis in the study looked at a multi-hospital database to compare 37,308 similar paired test results from ICU patients hospitalized at 178 medical centers in 2014 and 2015. This analysis, which was not adjusted, revealed similar discrepancies.
Dr. Sjoding said he and his colleagues began the study after hospitals in Ann Arbor, Michigan, which usually serve a predominantly white patient population, received a large influx of critically ill Covid patients from Detroit, many of whom were African American. “We found some inconsistencies with the arterial blood gas and we didn’t know what to do with it,” he said.
He recalled an article published in The Boston Review in August that looked at racial differences in the accuracy of pulse oximeter readings. The author of this article, Amy Moran-Thomas, became interested in the device after buying one when her husband fell ill with Covid. She unearthed scientific papers published in 2005 and 2007 that reported inaccuracies in pulse oximeter readings in dark-skinned individuals with low oxygen saturation.
Dr. Sjoding and his colleagues decided to conduct a study with data already collected during routine inpatient care in the hospital. “What we saw anecdotally was exactly what we showed in the thesis, that on the monitor in the patient’s room, the pulse oximeter reads ‘normal’, but when we get an arterial blood gas, the saturation on the gasoline was low “, he said.