Accuracy of blood tests for Alzheimer’s disease varies: study

The news this week that new blood test technology can reliably detect Alzheimer’s disease was met with excitement — but one dementia specialist is warning that the accuracy of these tests varies.

“Some of the blood tests are accurate and some are not, and doctors don’t know which tests to use,” explained Dr. Suzanne Schindler, an associate professor of neurology at Washington University in St. Louis. “With this head-to-head comparison, doctors now have more reliable information about which tests will best help them provide an accurate diagnosis to their patients.”

Schindler led a study comparing the accuracy of six commercial blood tests — four of which are clinically available.

Historically,invasive and expensive screening methods such as a spinal tap or brain scan were needed to diagnose Alzheimer’s, the most common type of dementia, which affects more than 5.8 million Americans.

The telltale biomarkers of the disease are brain-clogging protein clumps called amyloid plaques and accumulation of abnormal tau protein.

Schindler’s study included 392 people who provided blood samples within six months of undergoing brain scans. The participants were mostly around 80 years old — nearly half of them exhibited cognitive problems.

Each of the six tests measured the blood levels of one or more Alzheimer’s biomarkers, such as amyloid plaques, abnormal tau protein, reduced brain volumes and cognitive impairment.

One biomarker, used in four of the tests, was exceptionally accurate at identifying Alzheimer’s signs — a form of tau known as phosphorylated tau 217 (p-tau217).

“Some people thought that we might need to measure multiple biomarkers to get at the different features of Alzheimer’s disease,” said Kellen Petersen, an instructor in neurology at the WashU School of Medicine.

“That’s not what we found,” Petersen continued. “P-tau217 alone can do it all. It accurately predicted levels of amyloid and tau in the brain, brain volumes and cognitive symptoms. It was more accurate than any other biomarker, or even any combination of biomarkers, across the board.”

The four p-tau217 blood tests performed well regardless of how the biomarker was measured.

“We concluded that, to be used without a second test, blood tests need to be as accurate as [FDA]-approved cerebrospinal fluid tests, which are approximately 90% sensitive and specific at identifying Alzheimer’s disease in cognitive-impaired individuals,” Schindler said. “In this current study, the p-tau217 tests met that standard, but the others did not.”

Petersen presented the research Tuesday at the Alzheimer’s Association International Conference in Philadelphia.

The FDA has only approved two Alzheimer’s drugs, with others in the pipeline.

Leqembi and Kisunla have been shown to modestly slow worsening symptoms by targeting and removing amyloid plaques in the brain.

Both medications only work in the earliest stages of the disease, making early detection, like the kind promised by these blood tests, essential to effective treatment.

With Post wires