Blood test detects Alzheimer's pathology from age 40 with 97% accuracy

The FDA has cleared PrecivityAD2, a blood test that detects brain amyloid pathology in adults starting at age 40 with signs of cognitive decline, breaking a two-decade diagnostic gap in Alzheimer's identification. The test uses high-resolution mass spectrometry to measure two blood-based signals—amyloid protein ratios and tau protein ratios—which, triangulated together, deliver 97.6% accuracy on positive results and 93.1% on negative results when validated against PET scans and cerebrospinal fluid testing in 1,142 participants. Critically, its accuracy remained consistent across 12 common chronic conditions in older adults—atrial fibrillation, diabetes, kidney disease—eliminating the signal noise that has derailed previous biomarker efforts in real-world populations. This matters because current anti-amyloid therapies operate within a narrow treatment window where earlier intervention translates to irreversible neurological difference. By moving brain health screening from specialist referral into routine clinical visits—where cardiovascular and metabolic screening already live—the field inverts Alzheimer's logic: from a disease detected in crisis to a pathology intercepted in its preclinical phase.