The Centiloid Scale in Amyloid PET Imaging: Current Role in Alzheimer’s Disease Diagnosis, Treatment Planning, and Monitoring During Anti-Amyloid Therapy: A Clinical Perspective

Amyloid positron emission tomography (PET) has become a critical tool in the diagnosis and treatment of Alzheimer’s disease (AD). The Centiloid (CL) scale, a tracer/scanner-independent, standardized quantification unit introduced in 2015, transforms tracer- and scanner-specific standardized uptake value ratios (SUVRs) into a common metric anchored at 0 CL in young cognitively unimpaired individuals and 100 CL in patients with mild-to-moderate AD. This review synthesizes current evidence on the clinical role of the CL scale across three domains: (1) diagnostic classification, with established thresholds of <10 CL for amyloid negativity and >30 CL for high-certainty amyloid positivity; (2) treatment eligibility, where a 2024 Alzheimer’s Association Research Roundtable consensus of global experts recommended a 24–30 CL threshold for initiating lecanemab or donanemab therapy in patients with mild cognitive impairment (MCI) or mild AD dementia; and (3) longitudinal therapy monitoring, in which serial CL measurements provide objective evidence of amyloid clearance. We also review the emerging ‘gray zone’ (10–30 CL) as a distinct clinical entity with elevated progression risk, the critical role of CL quantification in complementing visual reads in borderline cases, technical limitations, and the future integration of CL in clinical practice. This review also critically addresses the ongoing debate on whether amyloid clearance represents a reliable surrogate for clinical benefit, strategies for managing discordant biomarker findings, and the practical feasibility of serial amyloid PET in routine care. With FDA approval of both lecanemab and donanemab, familiarity with the CL scale as a functional treatment biomarker is increasingly relevant for neuroradiologists and nuclear medicine physicians in the modern AD care pathway. As with all imaging modalities, the CL has physiologic and technical limitations. Although the CL scale was designed to reduce heterogeneity across tracers and scanner platforms, the impact of different commercial quantification software packages on CL output remains incompletely characterized. Consistent use of a single software platform for longitudinal monitoring in individual patients is therefore recommended.