A blood test already available to researchers can detect potential Alzheimer’s disease patients with very high accuracy, scientists say. According to a study published in the journal Jama Neurology, the simple blood test can detect p-tau217, a key biomarker for the disease, with up to 97% accuracy. The protein starts to build up in the brain up to 15 years before people with Alzheimer’s start showing symptoms, CNN reports. Since the test is far cheaper and less invasive than a spinal tap, experts say it could open the door to widespread screening for the disease—and when blood tests are negati…