New research raises alarm over Alzheimer’s blood test reliability

Early detection of Alzheimer’s disease (AD) can improve treatment outcomes, but current testing methods still have limitations.

Researchers have long relied on cerebrospinal fluid (CSF) biomarkers and positron emission tomography (PET) scans to identify amyloid and tau proteins, hallmarks of the disease. However, these tests are expensive and invasive, making them impractical for routine screenings.

Blood-based biomarkers have emerged as a promising alternative, offering a less invasive and more accessible diagnostic tool.

New advances in mass spectrometry and highly sensitive immunoassays have improved their accuracy, with blood tests now correlating more strongly with established diagnostic markers like tau PET scans and post-mortem brain pathology. Some can even predict cognitive decline before symptoms appear. However, while these developments show promise, blood-based tests still present significant challenges—especially for Black patients.

Recent research from Rutgers Health has revealed that current blood tests for Alzheimer’s may not be as reliable for Black patients as they are for white patients.

A key issue lies in the natural differences in biomarker levels between racial groups. CSF biomarkers such as total tau (t-Tau) and phosphorylated tau (p-Tau181) are consistently lower in Black individuals than in non-Hispanic white individuals, a pattern observed across different age groups.

Since blood biomarker tests are often calibrated using data from predominantly white populations, they may misdiagnose Black patients or fail to detect Alzheimer’s in its early stages.

William Hu, director of the Rutgers Center for Healthy Aging Research and senior author of a recent study published in Alzheimer’s & Dementia, warns against over-reliance on these tests.

“These tests are currently geared towards primary care physicians and directly to older adults concerned about cognitive performance,” Hu explained. “They may provide some value to primary care doctors who understand their limitations, but there is no reason for patients who have concerns about their memory to buy these tests, which cost $1,200 to $2,000 and are almost never covered by insurance.”

The study examined blood and CSF samples from 221 participants across diverse racial and ethnic backgrounds, including Black, non-Hispanic white, and ethnic Chinese individuals. Researchers found a 70% correlation between protein levels in spinal fluid and blood, but when they analyzed the test’s performance across racial groups, disparities became apparent.

For white participants, the blood test for p-Tau217—one of the most promising Alzheimer’s biomarkers—had a sensitivity of 90.3% and specificity of 81.1%. Sensitivity refers to the likelihood of correctly diagnosing individuals with the disease, while specificity measures the ability to correctly identify those without it.

However, for Black participants, sensitivity dropped to 73.7% and specificity fell to 72.5%. Even more striking was the difference in positive predictive value—the likelihood that a person actually has Alzheimer’s when the test comes back positive. In white participants, this value stood at 87%, while for Black participants, it was just 58%.

This means that Black patients who test positive for Alzheimer’s using current blood biomarkers may not actually have the disease at a much higher rate than white patients. At the same time, because of their naturally lower biomarker levels, many Black patients with Alzheimer’s might be overlooked entirely.

“For Black patients, it’s a double whammy,” Hu said. “Not only will you have a harder time using these proteins in the spinal fluid to diagnose Alzheimer’s disease in Black patients, you will further reduce the detection rate by relying on the blood tests.”

Interestingly, among Chinese participants, test performance was similar to that of white participants, suggesting that the issues may be specific to certain racial and ethnic backgrounds rather than a universal flaw in the technology.

One major reason for these disparities is the lack of diversity in Alzheimer’s research. Historically, clinical studies have focused on white populations, meaning that biomarker thresholds and diagnostic criteria were established without considering racial and ethnic differences. As more diverse populations participate in these studies, researchers are beginning to recognize and address these gaps.

However, much work remains to be done. Differences in Alzheimer’s biomarkers may stem from a variety of factors, including genetics, inflammation, and social determinants of health. For example, some researchers suspect that inflammatory responses to amyloid deposits in the brain may vary by race, potentially influencing biomarker levels in the blood and CSF.

Hu and his colleagues emphasize that these tests need significant refinement before they can be broadly used in clinical practice. “In another five to 10 years, these tests may get to the point where we can reliably use them, but right now, they are similar to some of the home COVID tests that had accuracy issues,” Hu said.

Until then, patients with memory concerns should seek a comprehensive neurological evaluation rather than relying on blood test results alone. According to researchers, about half of all Americans with Alzheimer’s remain undiagnosed, with early-stage cases being the most frequently overlooked. Since early detection is critical for slowing disease progression, improving diagnostic accuracy—especially for underrepresented groups—remains a top priority.

Despite these challenges, blood-based Alzheimer’s tests hold significant potential. They offer a more accessible and cost-effective alternative to invasive spinal taps and expensive PET scans, which are not widely available outside research settings. If researchers can refine these tests to account for racial and ethnic differences, they could revolutionize Alzheimer’s diagnostics.

The next steps in research involve gathering more diverse data and adjusting biomarker thresholds accordingly. By incorporating findings from broader racial and ethnic groups, scientists can work toward more equitable Alzheimer’s diagnostics that serve all patients effectively.

In the meantime, experts stress the importance of increasing participation in clinical studies among Black, Hispanic, and Asian communities. Expanding diversity in Alzheimer’s research will help refine diagnostic tools and ensure that future tests are both accurate and inclusive.

While a simple blood test for Alzheimer’s is not yet ready for widespread use, it remains a promising area of study. Until testing methods improve, the best course of action for individuals concerned about memory loss is to consult a neurologist for a full evaluation.

As science advances, researchers hope to develop more precise, accessible, and equitable diagnostic tools that work for everyone.

Note: Materials provided above by The Brighter Side of News. Content may be edited for style and length.

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