A common blood test measure may flag dementia risk years before memory problems appear. Researchers at NYU Langone Health analyzed the neutrophil to lymphocyte ratio, or NLR, in nearly 400,000 patients across two health care systems and found that a high ratio was associated with an increased risk of developing Alzheimer's disease and related dementias in people who showed no signs of cognitive impairment at the time.
Neutrophils are white blood cells that act as the immune system's first responders, surging during infection and inflammation. Because that surge shifts their proportion relative to lymphocytes, the NLR can be pulled straight from a complete blood count, the same routine test clinicians already order to check for infection and other immune conditions. No specialized assay, imaging, or spinal fluid sample is required.
That practicality is what makes the finding notable. Current tools for identifying people at elevated risk of Alzheimer's tend to be expensive or invasive, and a signal buried in existing lab work could in principle be read from records that millions of patients already have. The research team describes this as the first large-scale human investigation linking neutrophil measures to dementia risk.
The timing of the signal also raises a biological question. Since the neutrophil elevation showed up before any evidence of cognitive decline, the researchers argue it is worth investigating whether these cells are actively contributing to disease progression rather than simply reacting to it. An association in health records is not proof of cause, and that distinction is exactly what follow-up work will need to sort out.