A simple blood test already ordered for infections may quietly flag who will develop Alzheimer’s years before memory slips, according to two large health‑system studies.
Researchers at NYU Grossman School of Medicine combed through records from about 285,000 New York patients and 85,000 veterans, looking at the neutrophil‑to‑lymphocyte ratio (NLR) from routine complete blood counts taken after age 55 and before any dementia diagnosis. After adjusting for age, sex, race, ethnicity and major health conditions, higher NLR was tied to a 7 percent increase in recorded dementia risk in the New York cohort and a 21 percent increase among veterans.
The same pattern appeared in a separate analysis of nearly 400,000 patients from NYU Langone hospitals and the Veterans Health Administration, where scientists defined “high” NLR as any value above the median and found the link held for both short‑ and long‑term risk. Women and Hispanic participants showed a stronger association, though the data could not disentangle whether biology, access to care or other factors drove the disparity.
“Neutrophil elevation is happening before any evidence of cognitive decline, which makes a compelling case for studying whether neutrophils are actively contributing to disease progression,” said Tianshe (Mark) He, PhD, the data scientist who led both investigations.
Whereas NLR offers a cheap, widely available signal, it remains imperfect. The researchers stressed that the ratio is not a personal prediction tool but a population‑level clue that immune activity may sit closer to Alzheimer’s pathology than previously thought.
A third line of evidence points to a different blood marker that could someday outperform NLR. A team from Mass General Brigham followed 317 cognitively healthy volunteers aged 50 to 90 for an average of eight years, measuring plasma pTau217 alongside periodic amyloid‑beta and tau PET scans. Higher pTau217 levels anticipated future amyloid‑positive scans and tau tangles, even when current PET images appeared normal.
“What stood out in our study is that even when amyloid scans appear normal in the clinic, the pTau217 biomarker can identify individuals who later become amyloid‑positive,” said lead author Hyun‑Sik Yang, a neurologist at Mass General Brigham.
The pTau217 test still needs larger, more diverse samples before it can move from research labs to clinics, but it hints that blood‑based screening may eventually catch Alzheimer’s pathology a decade or more before symptoms arise.
How immune activity might influence brain disease
Alzheimer’s involves amyloid plaques and tau tangles that disrupt neural connections. Chronic inflammation can worsen this damage, as activated immune cells release chemicals that irritate nearby tissue. The neutrophil surge seen in elevated NLR reflects the body’s first‑responder response to infection or injury; if that response lingers, it may contribute to the hostile environment that accelerates neurodegeneration.
Why the risk signal varies across groups
Female and Hispanic participants consistently showed stronger links between high NLR and dementia risk, yet the studies could not pinpoint the cause. Possible explanations include genetic differences in immune regulation, variations in lifetime exposure to infections or stressors, and disparities in access to primary care that affect when blood tests are drawn and how results are interpreted.
What clinicians should know today
For now, an elevated NLR should not prompt Alzheimer’s screening on its own. Instead, it adds to the growing evidence that routine lab work can reveal subtle shifts in systemic immunity years before cognitive changes appear, reinforcing the value of tracking common biomarkers during preventive visits.
Can a routine blood test share me if I will get Alzheimer’s?
No. The neutrophil‑to‑lymphocyte ratio shows a statistical association with increased risk across large groups, but it is not accurate enough to predict disease for any single person.
Is the pTau217 blood test available at my doctor’s office?
Not yet. Researchers say larger, more diverse studies are needed to refine the test before it can be used clinically.
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