Alzheimer's disease diagnosis: An update and review of biomarkers, positron emission tomography, and emerging therapies.

Alzheimer's disease (AD) is a major global health burden whose diagnosis has shifted from syndromic assessment to a biologically grounded framework anchored in biomarkers. This review traces the evolution of diagnostic criteria, highlights the complementary roles of amyloid positron emission tomography (PET), tau PET, and fluid biomarkers, and discusses the growing clinical utility of blood-based tests-especially phosphorylated tau assays-with performance approaching that of cerebrospinal fluid (CSF) and PET measures. We also examine how the advent of disease-modifying anti-amyloid therapies has accelerated biomarker-guided pathways for patient selection, prognosis, and monitoring. Finally, we outline ethical issues surrounding preclinical diagnosis and survey future directions, including artificial intelligence (AI), neuroinflammation and synaptic markers, and personalized therapies. Collectively, these developments represent progress toward a precision-medicine model for AD, though major barriers to equitable and clinically meaningful implementation remain.