A Simple Blood Test Could Help Detect Alzheimer’s Years Before Symptoms
A new study published in September 2025 suggests that a routine blood test may one day reveal signs of Alzheimer’s disease long before memory problems or confusion appear. The research, carried out by scientists at the University of California, San Diego (UCSD), analyzed blood samples from 5,712 Hispanic and Latino adults aged 50 to 86. The results point to certain blood proteins that are strongly linked to memory loss and cognitive decline, even among people who seem healthy.
This is not just another incremental finding—it could mark an important step toward creating faster, less invasive, and more affordable ways to screen for Alzheimer’s compared to current methods like brain scans or spinal fluid tests.
What Exactly Did the Study Look At?
The UCSD team worked with data from the Study of Latinos–Investigation of Neurocognitive Aging (SOL-INCA). This is a sub-study of the Hispanic Community Health Study/Study of Latinos (HCHS/SOL), which is the largest and most detailed long-term project focused on Latino health in the United States.
The researchers set out to understand whether blood biomarkers—measurable substances in the blood that indicate changes in the body—could be linked to subjective cognitive decline. Subjective decline refers to when people notice changes in their memory or thinking skills, even if they perform normally on standard clinical tests.
Participants were asked questions based on the Everyday Cognition Scale (ECog-12), a short questionnaire designed to capture self-reported changes in areas like memory, planning, and overall thinking abilities.
Blood tests were then used to measure several key proteins that are known to play roles in brain health and Alzheimer’s disease:
- Neurofilament light chain (NfL) – a marker of nerve cell injury.
- Glial fibrillary acidic protein (GFAP) – a marker of brain inflammation.
- Phosphorylated tau protein (ptau-181) – a protein that accumulates in the brains of people with Alzheimer’s.
- Amyloid beta (Aβ42/40 ratio) – another hallmark protein often found in Alzheimer’s plaques in the brain.
The study also considered factors like age, gender, education, genetic risk (APOE status), cardiovascular health, and kidney function, making the analysis more robust.
Key Findings
The results were striking.
- Higher levels of NfL and GFAP were tied to more reports of decline in planning, memory, and overall thinking.
- Elevated levels of NfL and ptau-181 were linked specifically to memory concerns.
- Surprisingly, amyloid beta levels did not show any association with self-reported memory or thinking problems.
- Even participants who seemed cognitively healthy but had higher NfL levels reported noticing declines in how well they thought and planned.
This means that some of these proteins—especially NfL—might be able to pick up very early brain changes before the disease progresses to diagnosable Alzheimer’s.
Why This Matters
Currently, only one blood test has been approved by the U.S. Food and Drug Administration (FDA) to help with Alzheimer’s diagnosis: the Lumipulse G pTau217/Aβ42 plasma ratio test. While it works, it is expensive, only offered at select medical centers, and not practical for widespread screening.
If validated through future research, the approach studied at UCSD could provide a cheaper, faster, and more scalable option. For communities that are often underserved by healthcare systems, like Hispanic and Latino populations, this could be especially important.
Hispanic and Latino adults are already thought to have a higher risk of Alzheimer’s and related dementias, and projections show that this group may see the largest increase in cases over the coming decades. Yet, they are underrepresented in Alzheimer’s research. This study is notable for directly addressing that gap.
Strengths of the Study
One of the most important aspects of this research is its large and diverse sample size. Many past Alzheimer’s biomarker studies have primarily involved white participants, limiting the ability to apply findings broadly. By focusing on Hispanic and Latino adults from four major U.S. cities, the UCSD team has added valuable insight into how Alzheimer’s risk might appear in a different population.
Another strength is that the team accounted for social determinants of health (such as education and comorbidities) in their analysis. This allows a more realistic picture of how biomarkers interact with real-world health factors.
Important Limitations
Despite the encouraging results, the study does not mean we will see a routine Alzheimer’s blood test available in clinics tomorrow. Several important limitations must be acknowledged:
- Cross-sectional design: This was a snapshot in time, not a follow-up study. We don’t yet know if these biomarkers actually predict who will go on to develop Alzheimer’s or other dementias.
- Modest effect sizes: While the associations were statistically significant, they were not dramatic. Biomarkers are just one piece of a very complex puzzle.
- No link with amyloid beta: The absence of any association between amyloid beta and self-reported decline was surprising and highlights the need for more research.
- Generalizability: Although diverse, the study only included Hispanic and Latino participants from specific regions, so it may not fully represent all populations.
The researchers themselves caution that blood-based biomarkers should not replace existing diagnostic tools. Instead, they should be viewed as potential complements to current methods like imaging and cerebrospinal fluid testing.
What Comes Next?
The logical next step is to track participants over time to see if higher biomarker levels predict who will later develop mild cognitive impairment or Alzheimer’s disease. This type of longitudinal research will be critical to determining whether these blood proteins can truly serve as early-warning signals.
If proven, such a test could allow doctors to identify at-risk individuals earlier, enroll them in prevention programs, or monitor how well treatments are working.
A Quick Primer on Alzheimer’s and Biomarkers
Alzheimer’s Disease Basics
Alzheimer’s disease is the most common cause of dementia, affecting millions worldwide. It is characterized by progressive memory loss, difficulty in reasoning, and behavioral changes. In the brain, the two key features are amyloid plaques (clumps of amyloid beta protein) and tau tangles (twisted strands of tau protein inside nerve cells).
Why Biomarkers Matter
Traditional diagnosis often comes too late, after significant brain damage has already occurred. Biomarkers like NfL, GFAP, and ptau-181 could give doctors a head start, allowing them to detect changes in the brain before symptoms become disabling.
The Role of Amyloid and Tau
For decades, amyloid beta was seen as the main culprit in Alzheimer’s. However, growing evidence suggests that tau protein buildup and neuroinflammation might play more direct roles in cognitive decline. The UCSD study’s lack of association between amyloid beta and self-reported decline adds weight to this evolving view.
Other Conditions Affecting Biomarkers
It’s also important to note that proteins like NfL are not exclusive to Alzheimer’s. They can rise in other neurological conditions, including multiple sclerosis, traumatic brain injury, and Parkinson’s disease. This is another reason why these tests need further validation before being used widely.
Broader Implications
If these findings hold true, primary care doctors may one day order simple blood tests during routine checkups, especially for older adults at higher risk. This could revolutionize how we approach brain health—shifting from late diagnosis and damage control to early detection and prevention.
But until larger and longer studies confirm the predictive power of these biomarkers, they remain a promising but experimental tool. For now, the results give researchers, clinicians, and patients something hopeful to look forward to.
Final Thoughts
This study is exciting because it demonstrates that blood-based tests may soon become a practical way to detect Alzheimer’s before it robs people of their memories. By focusing on an underserved population and linking specific proteins like NfL, GFAP, and ptau-181 to self-reported cognitive decline, researchers are moving closer to making early detection accessible for all.
Still, the journey from research lab to doctor’s office is a long one. More work is needed to prove that these blood markers reliably predict Alzheimer’s and can be used to guide care. But given the rising number of dementia cases worldwide, this line of research is not just promising—it is urgent.
