A simple blood test shows promise as a way to detect Alzheimer’s disease, which could drastically improve the accuracy and speed of diagnoses.

Currently, Alzheimer’s is diagnosed via a mixture of memory and cognitive tests, as well as brain imaging and lab tests. But those tests are often aimed at ruling out other possible causes of symptoms, according to the National Institute on Aging. Even then, misdiagnosis is rampant; the researchers behind a new study wrote that up to 35% of patients in specialized clinics receive the wrong diagnosis. That number likely rises for patients who only visit a primary care facility. 

While some blood tests have shown promise as a diagnostic tool, they are hindered by their complexity. A new method, developed by an international team of physicians, may have solved that problem. 

Like previous blood tests for Alzheimer’s, the test was aimed at finding a biomarker in plasma—the liquid portion of blood—that indicates the presence of certain proteins associated with the disease. The biomarker, known as plasma phosphorylated tau 217 (or p-tau217), can also be found in cerebrospinal fluid, but extracting that is a more difficult process than blood. The test also looked at the ratio of two components of a plaque that forms in the brains of people with Alzheimer’s. If the p-tau217 was found in a sample along with a certain ratio of the plaque components, the researchers theorized it would lead to conclusive evidence that a patient had the disease. 

The patients were divided into groups and had their blood tests compared to results from a cerebrospinal fluid test. In a study published in the Journal of the American Medical Association, the researchers said their new method accurately detected signs of Alzheimer’s in around 90% of patients. 

The test was used on over 1,200 Swedish patients suffering from cognitive symptoms over the course of four years. 

While the early results are promising, the researchers note that more study is needed before the blood tests can be made widely available. Still, they acknowledged that early diagnosis could lead to much better outcomes thanks to promising new immunotherapy treatments currently being tested.