The Lumipulse G β-Amyloid Ratio assay is a cerebrospinal fluid (CSF) test used to assist in the diagnosis of Alzheimer disease in patients 55 years or older with cognitive impairment. In May 2022, the U.S. Food and Drug Administration authorized the test for marketing.¹ Lumipulse G is an automated system for bead-based immunoassays that measure biomarkers for Alzheimer disease, including amyloid β (Aβ)1-42, total tau, phosphorylated tau, and the Aβ1-42: Aβ1-40 ratio.² These proteins can accumulate to form amyloid plaques, which may be associated with Alzheimer disease.

Amyloid plaque formation decreases the Aβ1-42: Aβ1-40 ratio; thus, a low ratio supports the diagnosis of Alzheimer disease.³ In three independent cohorts of older adults with cognitive symptoms in Canada, Italy, and the Czech Republic, a cutoff value of 0.072 was established based on correlation with amyloid plaques detected on positron emission tomography (PET) scans and other immunoassay tests.^4–6