It's not easy to diagnose Alzheimer's: With doctors able to make that pronouncement based only on limited information such as patient and family interviews and mental acuity tests, the accuracy rate of such a conclusion hovers between 50% and 60%—"about the same as tossing a coin," notes the New York Times. That's why scientists are now excited about what they're calling the most sensitive blood test yet for the disease: one that identifies patients harboring a protein that's often an Alzheimer's indicator. The test, described in the journal Neurology, looked for the beta-amyloid protein—which in Alzheimer's patients gathers in clumps to create a cell function-disrupting plaque—in 158 "mostly cognitively normal" patients in their 60s and 70s. The test uses mass spectrometry, a process used in analytical chemistry that's very effective at hunting down beta-amyloid in blood.
The blood test in this study found beta-amyloid stockpiles in patients without Alzheimer's symptoms and whose brain scans didn't turn up beta-amyloid initially. Years down the road, however, those PET scans did finally locate beta-amyloid in those same patients with the positive blood tests, with 94% accuracy. There are caveats to this development: Beta-amyloid presence doesn't always lead to dementia, for example, and any practical use for the test would still be years away, but scientists are cautiously optimistic, especially if the test could be used to screen for patients who might benefit from preventative drugs. "If you are doing a prevention trial, you are looking for evidence of the disease that is silent," a UC San Francisco neurologist tells the Times. (Read more Alzheimer's disease stories.)