Alzheimer’s disease (AD) is best known for its cognitive symptoms, like memory loss and confusion. These symptoms can appear without warning, and from that point, gradual mental decline is unpredictable and nearly inevitable. But inside the brain of a patient, proteins accumulate into formations called amyloid plaques that interfere with signaling between brain cells. Amyloid build-up is not a sure sign of AD, but it is associated with a higher risk of the condition. Unfortunately, it is nearly impossible to get a close look at the brain until the patient is dead. Alternatives are brain scans or measuring protein levels in the fluid that surrounds the brain, but these are both difficult procedures, and especially impractical for regular monitoring of asymptomatic patients.

On the other hand, blood is easier to access, so researchers at Washington University devised a blood test that measures two fragments of amyloid protein in the blood—one of which tends to form the plaques found in the brain. When plaques form, it leaves less of that fragment to circulate in the blood. To measure how well the blood test results were reflected in the brain, they compared the results to a brain scan for amyloid plaques. They found that lower levels of plaque-forming amyloid in the blood was a good predictor of amyloid plaques in the brain scan, making accurate predictions 94% of the time. More importantly, when they looked at the same patients over time, patients with positive blood tests but no plaques on their brain scan were 15 times more likely to have amyloid plaques appear on brain scans up to a decade later.

Although this doesn’t point to strategies for better treatment or prevention, it suggests that windows into brain health might be more accessible than previously thought. With further studies that link blood test results to definitive AD diagnoses, AD might become as easy to detect as diabetes or high cholesterol, and improve the possibility of finding and providing a treatment long before symptoms occur.

Managing Correspondent: Aparna Nathan

Original articles: High-precision plasma β-amyloid 42/40 predicts current and future brain amyloidosis – Neurology

Media coverage: A Blood Test for Alzheimer’s? It’s Coming, Scientists Report – New York Times

A New Alzheimer’s Blood Test Proved 94% Accurate in Finding Brain Changes Related to the Disease – Time

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