New Test Can Accurately Predict 90 Percent of Alzheimer’s Cases

A new study has found a combined blood test for cognitive decline has a 90 percent accuracy rate in determining whether memory loss is due to Alzheimer’s disease. In comparison, neurologists and other memory specialists correctly diagnosed Alzheimer’s in 73 percent of their cases, while primary care doctors had even less success, with only a 61 percent accuracy rate.

One part of the test — called plasma phosphorylated tau 217, or p-tau217 — is one of several blood biomarkers scientists are evaluating for use in the diagnosis of mild cognitive impairment and early-stage Alzheimer’s disease. According to the researchers, the test measures tau protein 217, which is an excellent indicator of amyloid pathology. “Increases in p-tau217 concentrations in the blood are quite profound in Alzheimer’s disease,” said study coauthor Sebastian Palmqvist, MD, PhD, an associate professor and senior consultant neurologist at Lund University in Sweden. “At the dementia stage of the disease, levels are more than eight times higher compared with elderly without Alzheimer’s.”

In this study, the p-tau217 test was combined with another blood biomarker for Alzheimer’s called the amyloid 42/40 ratio, which measures two types of amyloid proteins, another biomarker of Alzheimer’s disease. The combination of the amyloid and tau tests, called the amyloid probability score, was the most predictive.

“The peptide p-tau217 is unique in that it can be detected only when amyloid plaques are present in the brain” said Maria Carrillo, PhD, chief science officer of the Alzheimer’s Association. “What that means to us scientifically is that when we’re measuring p-tau217, we’re measuring the neuronal damage from tau very early on in Alzheimer’s, but only when amyloid is already present. You’re not really measuring amyloid, but the test is telling you it’s there, and that’s been backed up with objective PET (positron emission tomography) scans that can see amyloid in the brain. It’s a beautiful marker for Alzheimer’s: If you don’t have amyloid present, you don’t have Alzheimer’s. If you have elevated tau in your brain, however, then we know that’s a sign of another type of dementia.”