By Dalia Elsaid
A blood test that costs a fraction of a brain scan could spare patients unnecessary procedures and give doctors more confidence in a diagnosis, according to a recent study.
Researchers followed 100 memory clinic patients who received a new blood test for Alzheimer’s disease. The test improved diagnostic confidence, reduced unnecessary imaging, and underscored the need for emotional support after results are shared.
Diagnosing Alzheimer’s disease has long relied on procedures that are costly, invasive, or difficult to access, including brain scans that cost thousands of dollars and spinal fluid tests many patients find uncomfortable. A study published this spring in Alzheimer’s & Dementia: Translational Research & Clinical Interventions suggests a simple blood draw may serve as a useful first step, especially for patients whose results are normal. Among patients with normal blood test results, the number of amyloid PET scans ordered dropped by about 75 percent after testing.
Researchers at the University of Pennsylvania enrolled 100 patients at a specialty memory clinic. Each patient received a blood test measuring levels of phosphorylated tau 181, or p-tau181. This is a “rule-out” test, meaning a normal result suggests there are no Alzheimer’s-related changes in the brain. The team then examined how the results shaped medical decisions and how patients and family members responded emotionally in the following months.
The clearest clinical impact appeared among the 19 patients with normal results. In that group, physicians were much more likely to revise their working diagnosis and much less likely to order an amyloid PET scan. This finding matters because amyloid PET scans are expensive and not widely available, especially in rural or lower-income areas.
For the 81 patients with elevated results, the picture was more complex. The test used in this study was designed to be highly sensitive, meaning designed to catch as many potential cases as possible, but it was not specific or precise enough to confirm a diagnosis on its own. A positive result raised concern without fully answering the question, and many of those patients still needed additional testing. Changes to diagnosis or treatment were less common than researchers had expected.
Even with those limits, physicians in both groups reported greater confidence in their diagnoses after reviewing the test results. This suggests the blood test added meaningful information, even when it did not directly change care.
Beyond the clinical findings, the study also examined how patients and caregivers emotionally processed the results in the months after testing.
Most patients and their family members or caregivers handled the news without serious distress, and none experienced severe psychological harm. Still, patients who received an elevated result showed higher anxiety levels two to three months later than those with normal results. The authors conclude that blood-based Alzheimer’s testing should be paired with patient education before testing and appropriate psychological support afterward.
One area where the test made little difference was behavior change. Patients in both groups were similarly unlikely to change their diet, exercise habits, or long-term plans in the months after receiving results. This suggests a test result alone may not prompt action and that ongoing clinical guidance may be needed.
The researchers note several limitations. The patient group was mostly White and well educated, and the high rate of Alzheimer’s cases in a specialty memory clinic may not reflect the broader population. The specific test used has also been replaced by newer, more accurate versions.
Even so, the authors argue the study points to an important future. As blood-based Alzheimer’s tests improve and become more widely available, they may expand access to diagnosis for patients who do not have a practical path to a brain scan or spinal fluid test, while also building the evidence needed for insurance coverage.
“Blood tests for Alzheimer’s disease have the potential to be highly impactful in both specialty and primary care,” said Kyra O’Brien, MD, lead author of the study, assistant professor of Neurology, and medical director of the Penn Medicine GUIDE Program. “The next step of this work is to bring Alzheimer’s blood tests into primary care to understand their value for patients who have not yet seen a memory specialist.”