Blood tests for Alzheimer's are needed to more widely diagnose the brain-wasting disease and understand its prevalence, but it will be another couple of years before they become an everyday tool, medical experts and company executives say. Blood testing is initially likely to be used to rule out Alzheimer's, with positive results signaling the need for more advanced diagnostics. Several Alzheimer's blood tests are in the works – and one is already being sold to consumers – but none have been established as accurate, formally approved by regulators or reimbursed by insurers.