Diagnostics that can identify biomarkers of disease in the blood are helping speed drug trials for intractable conditions like Alzheimer's.Why it matters: Blood biomarker diagnostics can help pharmaceutical companies identify the right patients to enroll in drug trials for difficult-to-diagnose neurological conditions without resorting to more expensive and invasive methods like brain scans or spinal taps.Get market news worthy of your time with Axios Markets. Subscribe for free.Driving the news: The FDA is due to make a decision by June 7 on Biogen's aducanumab drug, which if approved would be the first drug ever authorized to slow the course of a form of dementia found in some 6 million Americans.The decision will be fraught — an advisory panel to the FDA declined to endorse the drug in November, saying there was not enough evidence of its effectiveness.Between the lines: Potential Alzheimer's drugs have continually disappointed in trials, in part because identi