No single diagnostic test currently exists for Alzheimer’s disease. Standard Alzheimer’s disease testing is based on a battery of tools and assessments, including structural imaging to rule out other conditions that may cause similar symptoms but require different treatments. The most widely used biomarker in clinical studies for Alzheimer’s disease diagnosis is Aβ measured in cerebrospinal fluid (CSF) and by positron emission tomography (PET) .
Alzheimer’s disease CSF is characterized by an approximate 50% reduction in the concentration of Aβ42 , and increased diagnostic accuracy can be achieved by measuring CSF Aβ42/Aβ40 ratios. This ratio is nearly completely concordant with amyloid PET imaging, which has undergone extensive standardization . However, CSF sampling is an invasive procedure, and amyloid PET is expensive, has limited availability, and is associated with a non-negligible radiation exposure . Therefore, the identification and validation of blood biomarkers for Aβ pathology would greatly improve diagnostics for patients with cognitive impairment. Plasma Aβ42/Aβ40 ratios have already been shown to reflect cerebral Aβ pathology with high accuracy compared to amyloid PET and CSF Aβ42/Aβ40 ratios .
PrecivityAD is the first approved blood test designed to aid in Alzheimer’s disease detection decades before symptom onset. This method quantifies plasma Aβ and APOE levels by liquid chromatography with tandem mass spectrometry . The results, which also account for a patient’s age, provide a probability score of a patient having an amyloid-positive brain scan.
CSF tau may also be regarded as a predictive marker of Alzheimer’s disease-type neurodegeneration . Standardization work for tau imaging is still ongoing, but it could become a valuable tool for evaluating the efficacy of amyloid, tau, or combination therapy. Furthermore, tau PET has demonstrated the ability to detect the pharmacodynamic effects of disease-modifying drugs targeting both Aβ and tau pathology .