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Alzheimer’s is a difficult disease to diagnose. The clinical markers—plaques of amyloid proteins and tangles of filamentous tau proteins building up in the brain—are best measured with PET scans, which are expensive and not widely available.
The search for easier, more reliable ways to detect the disease has been going on for years and the FDA recently approved a blood test for people over the age of 55. Now, new research published in Nature Medicine shows promise not for just detecting Alzheimer’s, but predicting when the onset of symptoms will occur.
Neuroscientists from Washington University took blood samples from 600 people aged 62 to 78 who weren’t experiencing cognitive impairment. By measuring the levels of a phosphorylated version of tau, p-tau217, they were able to create a model capable of estimating the onset of Alzheimer’s symptoms within a margin of error of three to four years.
“Amyloid and tau levels are similar to tree rings—if we know how many rings a tree has, we know how many years old it is,” study author Kellen K. Petersen said in a statement. “It turns out that amyloid and tau also accumulate in a consistent pattern and the age they become positive strongly predicts when someone is going to develop Alzheimer’s symptoms. We found this is also true of plasma p-tau217, which reflects both amyloid and tau levels.”
Read more: “What Alzheimer’s Feels Like from the Inside”
It’s encouraging news for the millions of Americans at risk of developing Alzheimer’s, but it comes with some important caveats. Concerned about false positives, many experts are raising the alarm about widespread blood testing in people who haven’t shown symptoms of the disease. Blood tests, they say, should only be one piece of a more comprehensive diagnostic protocol.
Even though this latest test will need more fine-tuning before it’s ready for prime time, it can still be used in clinical trials.
“In the near term, these models will accelerate our research and clinical trials,” study author Suzanne E. Schindler said. “Eventually, the goal is to be able to tell individual patients when they are likely to develop symptoms, which will help them and their doctors to develop a plan to prevent or slow symptoms.”
A number of factors have been associated with a delayed progression of the disease—like a healthy diet, active lifestyle, and social engagement—but there are only two recently approved treatments to delay Alzheimer’s when it’s caught early.
It’s a big step in the right direction, but not exactly a miracle breakthrough. 
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Lead image: GerryShaw / Wikimedia Commons
