Credit: Linda Bartlett/National Cancer Institute, via Wikimedia

Three experimental blood tests used to identify people in early stages of Alzheimer’s disease perform differently in Black individuals compared to Whites, according to a new study from Washington University School of Medicine in St. Louis.

A fourth blood test, however, was equally effective at detecting early Alzheimer’s disease regardless of the race of the person being tested. That was the PrecivityAD test, which is available in the U.S. and Europe through C2N Diagnostics, which is a Washington University startup based in St. Louis.

The study was reported in Neurology this week. The lead author is Suzanne Schindler, an associate professor of neurology.

“When you use a limited study population—as, unfortunately, scientists have traditionally done in Alzheimer’s research—and then try to apply the results to everyone, including people of diverse backgrounds, you could exacerbate health inequities,” said Schindler. “My hope is that this paper will help illustrate the need to increase the diversity of participants in Alzheimer’s studies.”

Cutoffs between normal and abnormal test scores are usually set based on predominantly white volunteers. Tests that perform differently in Black compared to white populations put Black patients at disproportionate risk of misdiagnosis and receiving inappropriate medical care.

Most people are diagnosed with Alzheimer’s only after they become forgetful and confused. Such cognitive symptoms arise relatively late in the course of the disease, a decade or more after the brain first begins to change. Scientists are working to identify people earlier using blood tests that detect blood biomarkers. But the field of Alzheimer’s biomarker research is based on data collected from groups of mostly white participants, raising concerns about whether such tests will be equally valid in diverse populations.

This study was not designed to find the reason some Alzheimer’s biomarkers lead to different results in Black compared to white individuals, but the presence of other health conditions could play a role. These researchers found that Black participants were more likely than whites to have high blood pressure (67% versus 45%) and diabetes (28% versus 5%). Both conditions are linked to Alzheimer’s disease and may influence performance of biomarker tests, the researchers said.

They also analyzed the accuracy of the PrecivityAD test and blood tests for two other proteins—neurofilament light protein and two forms of the protein tau—in 76 pairs of Black and non-Hispanic white participants. The participants were matched on age, gender, cognitive status and presence of the high-risk genetic variant of APOE. More than 90% of individuals had no cognitive impairment. The researchers determined whether each individual had the brain changes of Alzheimer’s disease using brain scans, analyzing the cerebrospinal fluid that surrounds the brain and spinal cord, or both.

Only the PrecivityAD test accurately classified people by Alzheimer’s status regardless of self-identified race. The other three blood tests were not as accurate at classifying people by Alzheimer’s status. Worse, they also performed differently in Black individuals compared to white individuals.

The PrecivityAD test uses high-resolution mass spectrometry to measure the ratio of the Alzheimer’s proteins amyloid beta 42 and amyloid beta 40, as well as apolipoprotein E (APOE), a protein that affects risk for Alzheimer’s disease.

“Race norming,” or calibrating tests separately for each race, is not a satisfactory solution to the problem of differences in biomarkers across racial groups, Schindler and Karikari said. Such a practice can create or worsen racial disparities.

“Rather than trying to adjust for race in some way, it would be better to use tests that perform equally well in all individuals,” Schindler said.

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