Alzheimer’s Blood Test Could Soon Replace Invasive Spinal Taps and Brain Scans

Historically, Alzheimer’s disease was primarily diagnosed based on observable symptoms, particularly when individuals started exhibiting memory and cognitive difficulties. However, it's been revealed through research that up to a third of individuals diagnosed with Alzheimer's based solely on cognitive symptoms have been incorrectly diagnosed, with their symptoms stemming from other causes. The accurate identification of Alzheimer’s disease has become increasingly crucial, especially since the introduction of the first treatments that can slow the disease's progression, along with other promising drugs currently in development. These treatments are potentially more effective when administered early, highlighting the need for early detection of the disease. Therefore, to qualify for Alzheimer's therapies, patients must show cognitive impairment and test positive for amyloid plaques, which are distinctive to Alzheimer's. Techniques like amyloid positron emission tomography (PET) brain scans, cerebrospinal fluid analyses, and blood tests are used to detect brain amyloid plaques. However, these are only employed for individuals already showing cognitive symptoms and not for asymptomatic individuals.

Now, a study by researchers at Washington University School of Medicine in St. Louis (WUSM, St. Louis, MO, USA) and Lund University (Lund, Sweden) has demonstrated that a blood test can diagnose Alzheimer's disease pathology as accurately as cerebrospinal fluid tests and brain scans. This is true even for patients with mild symptoms and can detect molecular signs of Alzheimer's in the brain before symptoms appear. This groundbreaking blood test could potentially replace more costly and invasive methods like brain scans and spinal taps for identifying Alzheimer’s indications in the brain. Developed by researchers at Washington University, this blood test employs a highly sensitive technique to measure Alzheimer's protein levels in the blood. It works by using mass spectrometry to assess the ratio of two amyloid forms in the blood and was granted Breakthrough Device designation by the FDA in 2019.

Image: The blood test could make early Alzheimer’s diagnosis and treatment accessible to more people (Photo courtesy of 123RF)

Following this, the researchers have introduced a second blood test focusing on the impact of amyloid accumulation on another brain protein, tau. Amyloid presence in the brain alters the levels of various tau protein forms both in the brain and the blood. The ratio of phosphorylated tau-217 (ptau-217) to unphosphorylated tau in the blood is a reliable indicator of brain amyloid levels. In their latest study, the researchers compared four different tests for their ability to detect amyloid in the brain: the ptau-217 blood test and three FDA-approved cerebrospinal fluid tests. They assessed these tests using blood and cerebrospinal fluid samples from two groups of volunteers - one cohort of 1,422 people and a second cohort of 337 people, including individuals with very mild and mild cognitive symptoms, as well as healthy individuals for comparison. The accuracy of these tests was determined by comparing their results with the gold standard of PET brain scans for amyloid and tau tangles.

The findings showed that the ptau-217 blood test matched the FDA-approved cerebrospinal fluid tests in accurately identifying individuals with amyloid buildup, with all tests achieving accuracy rates between 95% and 97%. In a further analysis focusing on the detection of tau tangles in the brain, the ptau-217 blood test outperformed cerebrospinal fluid tests, achieving accuracy rates ranging from 95% to 98%. An additional analysis focusing on healthy participants revealed that the ptau-217 blood test accurately detected those with amyloid plaques in their brains, showing equal accuracy in identifying amyloid presence in both symptomatic and asymptomatic individuals. Research has indicated that individuals without cognitive issues but positive for amyloid are at a high risk of developing cognitive impairments in the coming years.

“The accuracy of this blood test now enables us to diagnose the presence of Alzheimer’s disease pathology with a single blood sample,” said Randall J. Bateman, MD, the Charles F. and Joanne Knight Distinguished Professor of Neurology at Washington University. “This advance will increase accurate diagnoses for many patients.”

“In the near future, this type of blood test will replace the need for costly and less accessible cerebrospinal fluid and PET imaging tests in specialist memory clinics,” added Oskar Hansson, MD, PhD, a professor of neurology at Lund University.

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