New Alzheimer’s Blood Test 94% Accurate

Megan Brooks

August 02, 2019

A new blood test to detect brain changes emblematic of early Alzheimer’s disease (AD) has moved one step closer to reality and could be a “game changer” for the field.

Researchers found that measuring the ratio of β-amyloid (Aβ) 42 and Aβ40 in blood using a high-precision assay is 94% accurate in diagnosing brain amyloidosis, using amyloid PET or CSF phosphorylated (p-tau) 181/Aβ42 as reference standards.

“Right now we screen people for clinical trials with brain scans, which is time-consuming and expensive, and enrolling participants takes years,” senior investigator Randall J. Bateman, MD, professor of neurology, Washington University School of Medicine in St. Louis, said in a statement.

“But with a blood test, we could potentially screen thousands of people a month. That means we can more efficiently enroll participants in clinical trials, which will help us find treatments faster, and could have an enormous impact on the cost of the disease as well as the human suffering that goes with it,” he added.

The study was published online August 1 in Neurology.

Easy Screening Tool

Using an immunoprecipitation and liquid chromatography–mass spectrometry assay, the researchers measured Aβ42/Aβ40 in plasma and CSF samples from 158 older, mostly cognitively normal individuals (94% with Clinical Dementia Rate [CDR] = 0) that were collected within 18 months of an amyloid PET scan.

Plasma Aβ42/Aβ40 correlated highly with amyloid PET status (receiver operating characteristic area under the curve [AUC], 0.88; 95% confidence interval [CI], 0.82 – 0.93) and CSF p-tau181/Aβ42 (AUC, 0.85; 95% CI, 0.79 – 0.92), the researchers report.

The combination of plasma Aβ42/Aβ40, age, and apolipoprotein (APOE) ε4 status had “very high” correlation with amyloid PET (AUC, 0.94; 95% CI, 0.90 – 0.97), “suggesting that plasma Aβ42/Aβ40 may be used as a screening tool for those at risk of AD dementia,” the researchers write.

In addition, individuals with a positive plasma Aβ42/Aβ40 but negative amyloid PET scan have a 15-fold higher risk of converting to amyloid PET-positive (P = .01).

“The sensitivity of the plasma Aβ42/Aβ40 assay to amyloid PET-negative individuals who convert to amyloid PET-positive suggests that plasma Aβ42/Aβ40 becomes positive earlier than the established amyloid PET threshold used for this study,” Bateman and colleagues note in their report.

“Therefore, a positive plasma Aβ42/Aβ40 with a negative amyloid PET scan may represent early amyloidosis rather than a false-positive result in some individuals,” they add.

As reported by Medscape Medical News, the study builds on earlier work by the same researchers.


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