Some of the populations with the highest risk for Alzheimer’s disease remain greatly underrepresented in clinical trials—and a new study helps explain why. USC researchers found that cognitively unimpaired individuals from African American, Hispanic and Asian participants were less likely to have levels of p-tau217 in the blood that indicate elevated amyloid in the brain, showing they lacked the early signs of Alzheimer’s disease that would allow them to participate in a trial of lecanemab.  The study leverages a new and improved blood test, p-tau217, that more accurately detects early signs of Alzheimer’s disease. Rising levels of p-tau217 are strongly linked to the buildup of amyloid, which disrupts brain activity in Alzheimer’s disease, and the p-tau217 test is increasingly used to determine who qualifies for treatment studies. The study included 6,437 adults, ages 55 to 80, recruited from 75 sites across the country for AHEAD 3-45, a clinical trial designed to test the safety and efficacy of lecanemab, which removes amyloid from the brain. Of those, 4,832 identified as non-Hispanic white, 877 as Hispanic white, 511 as non-Hispanic Black, 155 as non-Hispanic Asian and 62 as Hispanic Black. All participants were cognitively unimpaired. Using blood tests for p-tau217, the researchers found that non-Hispanic white participants were more likely than other groups to meet the threshold for inclusion in Alzheimer’s disease clinical trials. Those who identified as Hispanic Black, Hispanic white, non-Hispanic Asian and non-Hispanic Black were significantly less likely to qualify to participate. The study provides a valuable opportunity to better understand risk for future Alzheimer’s disease related dementia across populations. Those insights have important implications for the development of prevention therapies that will be necessary to address the needs of all individuals at risk of dementia.