Test code(s): 11786, 12563, 13825, 13690, 94627, 94628, 92433, 10642
The combination of beta amyloid 42/40 and p-tau181 are utilized to detect AD pathology changes (amyloid plaques and neurofibrillary tangles) characteristic of Alzheimer’s disease. The presence of beta amyloid in the absence of a positive p-tau181 result typically occurs early in the Alzheimer’s disease continuum.
A beta amyloid ratio below 0.160 indicates a higher likelihood of having a positive amyloid PET scan. In a memory clinic cohort, a beta amyloid ratio of 0.169 to 0.160 correlated with 15% of patients having a positive amyloid PET scan, while a ratio of 0.159 to 0.150 correlated with an 85% chance of patients having a positive amyloid PET scan1.
The presence of APOE e4, particularly in patients who are homozygotes, indicates an increased risk for the development of ARIA with anti-amyloid treatment2.
A borderline CSF result typically is the result of a patient with underlying amyloid pathology, but the test result is more consistent with having mild cognitive impairment (MCI) rather than with full-blown Alzheimer’s disease3.
Patients with a positive beta amyloid 42/40 ratio and a negative PET scan are often earlier in the disease continuum. A recent study showed that patients with a positive 42/40 ratio and a negative PET scan are consistent with AD pathology on MRI4.
References
This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on the physician’s education, clinical expertise, and assessment of the patient.
Document FAQS.303 Version: 0
Version 0 effective 08/28/2024 to present