Combining two blood tests improved diagnosis of Alzheimer's disease and reduced overdiagnosis in people with asymptomatic Alzheimer's disease, according to a prospective study cohort.[2] Blood tests measuring the protein p-tau217 show high accuracy in detecting brain changes associated with Alzheimer's disease, with experts estimating their accuracy in differentiating other types of dementia at 89 to 98 percent.[7] A February 2026 study published in the journal Nature Medicine showed that the test was able to predict the onset of Alzheimer's symptoms within 3–4 years.[2] Blood tests have been shown to have a good negative predictive value, meaning they are effective at accurately determining who does not have amyloid disease—in low-prevalence settings, a negative result is 97.9 percent reliable.[3] These tests are cheaper and more accessible than brain imaging or cerebrospinal fluid sampling, which can significantly improve the approach to Alzheimer's disease prediction.[2] However, experts emphasize that blood tests should only be used in patients with symptoms of cognitive decline, not in cognitively healthy people.[4]