Blood test of p-tau217 showed a similar or better ability in detecting Alzheimer’s disease-related structure changes in the brains of individuals with impaired cognitive ability, compared with cerebrospinal fluid test. The researchers suggest that p-tau217 blood test may replace positron emission tomography or cerebrospinal fluid test, the methods currently used in research and the clinic. 

Physicians commonly use positron emission tomography and cerebrospinal fluid test as part of the diagnosis process for Alzheimer’s. Positron emission tomography for visualizing the accumulations of markers of Alzheimer’s in the brain. Cerebrospinal fluid test for measuring the levels of the markers in the fluid from inside and around the brain and spinal cord. The commonly used markers are two proteins called amyloid beta and tau that can indicate the Alzheimer’s-related brain structure changes.

Blood test is a well-established and easily accessible diagnostic technique. Using blood test to measure the levels of the markers that are accurate, specific, and sensitive to Alzheimer’s could improve early detection of the condition. Currently, study evidence on the diagnostic ability of blood-based biomarker that is similar to positron emission tomography or cerebrospinal fluid test is insufficient. 

To add evidence and move the use of blood-based biomarker closer to the clinic, researchers from Lund University and Washington University investigated whether  the blood test can perform as good as the cerebrospinal fluid test.  

They included one group of elderly participants from Sweden and another group from the United States. In the Swedish group, 702 participants had impaired cognitive ability. In the American group, 50 were with this condition. The average age of the participants from the two groups were both around 69. 

The researchers collected cerebrospinal fluid and blood samples from the participants to measure the biomarkers’ levels. The biomarkers included amyloid beta40, amyloid beta42, p-tau181, and p-tau217. They also carried out positron emission tomography among the participants. 

In both the Swedish and American group, the researchers calculated the diagnostic ability of blood p-tau217 identifying the participants with amyloid beta positive in the brains was 97%. This level of ability is similar to that of cerebrospinal fluid tests validated in the clinic.

When they used blood p-tau217 to identify tau positive in the participants’ brains in the Swedish group, its diagnostic ability was 95%, and 98% in the American group. The blood p-tau217 in both groups showed better ability than the cerebrospinal fluid tests. 

“The high performance of plasma %p-tau217 in classifying amyloid beta and tau positron emission monography status indicates that this blood-based biomarker may be able to replace approved cerebrospinal fluid test and positron emission monography measures in the diagnostic workup of Alzheimer’s disease,” wrote the researchers. 

In another study recently published in the journal JAMA Neurology, a different team of researchers found similar results. They showed that blood p-tau217 accurately identified amyloid beta and tau positive in the brains of the participants. The accuracy of this blood test reached the range of 92-96% for identifying amyloid beta positive, and 93-97% for identifying tau positive. This accuracy levels were also similar to that of the cerebrospinal fluid tests. 

Findings from these two studies add evidence and confidence that p-tau217 is a potential blood-based biomarker that physicians may use officially in their clinical practice. It would reduce the need for using positron emission monography and cerebrospinal fluid tests. Therefore, it could make the diagnosis process of Alzheimer’s more accessible globally for physicians, at-risk individuals, as well as people with the condition. 

This study was published in Nature Medicine. Image credit: Canva

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