A new blood-based screening algorithm dramatically reduced the number of unnecessary PET scans needed to recruit patients at risk of Alzheimer’s disease for a clinical trial, according to research from scientists at the Keck School of Medicine of USC. Known as AHEAD 3-45, the clinical trial is a phase 3 international study testing whether earlier treatment with an approved drug for Alzheimer’s disease, known as lecanemab, could lead to better outcomes. Lecanemab removes sticky amyloid-beta protein aggregates that accumulate in the brain and are associated with the progression of Alzheimer’s disease. The drug can slow the clinical progression of the disease by about 30% but is currently prescribed only for patients who already have symptoms of cognitive decline. The AHEAD 3-45 trial specifically targets people with buildup of amyloid-beta, which happens early in the progression of Alzheimer's disease, sometimes decades before symptoms of cognitive impairment appear. However, only about 30% of cognitively healthy adults over 65 have amyloid levels high enough to qualify for trials like AHEAD. A major hurdle for recruiting patients to the trial is identifying and screening large numbers of people who may have hallmarks of the disease, but don’t yet have obvious symptoms such as memory loss. Before blood plasma screening was introduced, candidates for the AHEAD 3-45 trial had to navigate a screening process that could take up to three months from first visit to enrollment. After undergoing positron-emission tomography (PET), a costly imaging scan considered the gold standard for Alzheimer’s diagnosis, more than 70% of candidates would learn that they were ineligible for the trial. When the algorithm was used in recruiting participants for the study, it cut the rate of people who received a PET scan but did not qualify for the trial from more than 70% to 31%.