Scientists have discovered a blood test to diagnose Alzheimer's disease without the need for expensive brain imaging or the painful lumbar puncture (CSF sample of cerebrospinal fluid), where a sample of cerebrospinal fluid is taken from the spine. If validated, the test could allow faster diagnosis of the disease, meaning treatments could begin sooner. 
The Guardian he says:
Current guidelines recommend detecting three distinct markers: abnormal accumulations of amyloids and proteins, and neurodegeneration – the slow and progressive loss of neuron cells in specific areas of the brain. This can be done through a combination of brain imaging and CSF analysis. However, a lumbar puncture can be painful and many people may experience headaches or back pain after the procedure, and brain imaging is expensive and time-consuming to schedule.
Although current blood tests can accurately detect abnormalities in amyloid proteins, detecting brain-specific markers of nerve cell damage has been more difficult.
Professor Thomas Karikari at the University of Pittsburgh, Pennsylvania, and his colleagues around the world focused on developing an antibody-based blood test that would detect a specific form of the brain-derived tau protein specific to the disease. Alzheimer's.
They tested it in 600 patients at various stages of Alzheimer's disease and found that the levels of the protein correlated directly with the levels of tau that showed up in the CSF test. Thus they could reliably distinguish Alzheimer's from other neurodegenerative diseases.
The survey was published in Brain magazine.
