Blood test could detect the onset of dementia decades before symptoms are noticed, study finds

A simple blood test could detect the onset of dementia almost two decades before symptoms are noticed, according to a new study. Researchers have long known that dementia sufferers have higher levels of a certain protein that leaks into the cerebrospinal fluid after brain cells die. But they could not work out how to measure it without invasive, expensive spinal taps. In a new study, scientists say they can now detect this protein in the blood and that levels of it rise at the same speed that the brain loses neurons and begins shrinking. The blood test that looks for the protein would be performed in middle-age, well before most are diagnosed with Alzheimer's disease.