Amyloid-beta 42/40 Ratio, CSF

AB-42/40 Ratio, Beta-amyloid 42/40 Ratio, AB 1-42/1-40 Ratio, Aβ-42/40 Ratio

7 Days

Chemiluminescent Enzyme Immunoassay (CLEIA)

Methodology: Fujirebio Lumipulse G, Chemiluminescent Immunoassay (CLEIA). A result ≥ 0.073 is interpreted as negative, consistent with a negative amyloid PET scan, and indicates a low likelihood that the patient’s cognitive impairment is due to Alzheimer’s disease (AD).

A result between 0.059 and 0.072 is considered likely positive, suggesting probable consistency with a positive amyloid PET scan. However, this range carries greater uncertainty, and while it may indicate amyloid pathology, does not establish a definitive diagnosis of AD or any other cognitive disorder.

A test result ≤ 0.058 is interpreted as positive, consistent with a positive amyloid PET scan, and satisfies established criteria for amyloid biomarker positivity, reflecting impaired Aβ-42 clearance and probable amyloid plaque deposition. However, this result must be interpreted in clinical context and does not alone confirm a diagnosis of AD or another cause of cognitive decline. Additional biomarkers, including phosphorylated tau (p-tau 181 or p-tau 217), total tau, neurofilament light chain (NfL), and neurogranin can enhance diagnostic confidence, aid in disease stratification, and support prognostic assessment.

Accredited NRL Laboratory

Weekly

A key neuropathological feature of Alzheimer’s disease (AD) is the accumulation of amyloid-beta plaques in the brain. This assay measures two beta-amyloid peptides: Amyloid-beta 42 (AB 42 aka Aβ1-42) and Amyloid-beta 40 (AB 40 aka Aβ1-40). Under normal conditions, AB-40 is present at higher concentrations than AB 42. In AD, reduced clearance or increased production of AB 42 leads to its aggregation into plaques and subsequent neurotoxicity. In contrast, AB 40 is less prone to aggregation and typically remains unchanged in patients with AD compared with healthy individuals.

Multiple studies have shown that the CSF AB 42/AB 40 ratio improves diagnostic accuracy for AD compared with AB 42 alone. The ratio shows high concordance with amyloid PET imaging and is effective in distinguishing AD-related amyloid deposition from other causes of mild cognitive impairment or dementia. Additionally, use of the AB 42/40 ratio helps reduce the impact of preanalytical variability that can affect AB 42 measurements, improving result reliability.

CSF

Minimum 0.5 mL

Sarstedt sterile polypropylene tubes

Preferably, the lumbar puncture should be performed in the morning.

Perform the lumbar puncture at the L3/L4 or L4/L5 intervertebral space. Collect the cerebrospinal fluid in an appropriate polypropylene tube and transport it frozen at –20°C.