Blood tests are evaluated by comparing how often the results of the test align with an amyloid PET scan or spinal tap. There is substantial variation in the accuracy of individual blood tests, which means that some are less accurate than the spinal taps. Current guidelines developed by an Alzheimer’s Association-convened working group outline that for a blood test to be used as a standalone confirmatory tool by specialists, it needs at least 90 percent sensitivity and specificity.