Is there a blood test for diagnosing Alzheimer's disease?

From the Guidelines

Yes, there are blood tests for diagnosing Alzheimer's disease, specifically measuring amyloid-beta and tau proteins in the blood, which have shown acceptable performance in recent studies. These blood biomarker (BBM) tests have unique advantages over amyloid PET and CSF tests, including being safe, acceptable to most patients, and easily scalable for widespread use in clinical practice 1. The most promising BBM measures for amyloid status include the Aβ42/Aβ40 ratio and tau phosphorylated at different sites, such as p-tau181, p-tau217, and p-tau231, with assays of plasma levels of p-tau217 or the ratio of p-tau217 to non-phosphorylated tau showing high accuracy in predicting amyloid status, with receiver operating characteristic area under the curve (AUC) values of 0.92-0.98 1.

Key Points

• BBM tests are now widely used in AD research studies and clinical trials, and multiple tests are clinically available 1
• The accuracy of different BBM tests varies widely, with mass spectrometry-based assays typically being more accurate than immunoassays 1
• Assays of the plasma Aβ42/Aβ40 ratio have AUCs of 0.70-0.85 in classification of amyloid PET status, while assays for phosphorylated tau species perform even better, with AUCs of 0.92-0.98 1
• BBM tests offer advantages over more invasive procedures like lumbar punctures and expensive brain imaging, and can be used to support diagnosis in conjunction with clinical evaluation, cognitive testing, and brain imaging 1

Clinical Use

• BBM tests are not intended as standalone diagnostic tests for symptomatic AD, but rather as part of a comprehensive assessment, including medical evaluation, neurological examination, cognitive testing, and laboratory testing for common reversible causes of cognitive impairment 1
• The use of BBM tests in clinical practice is still evolving, and their performance and limitations need to be carefully considered when interpreting results 1

From the Research

Blood Tests for Alzheimer's Disease

• There are several blood tests being developed and researched for the diagnosis of Alzheimer's disease, including those that detect amyloid and tau biomarkers 2, 3, 4.
• These blood tests have shown promise in identifying Alzheimer's disease pathology, with some studies demonstrating high accuracy in detecting amyloid and tau biomarkers 2, 4.
• The use of blood tests for Alzheimer's disease diagnosis is considered a significant milestone, but it is essential to use them in conjunction with clinical evaluation to avoid misinterpretation 3.
• Some of the challenges associated with blood tests for Alzheimer's disease include the need for standardization, accessibility, and understanding of individual assay information and methodology 2, 5.
• Researchers are continuing to develop and refine blood tests for Alzheimer's disease, with the goal of creating a reliable, fast, and affordable method for early diagnosis 4, 6.

Types of Blood Tests

• Amyloid-based blood tests, such as the PrecivityAD™ test, are available for clinical use and have shown promise in detecting Alzheimer's disease pathology 3.
• Phosphorylated tau blood tests are also being developed and may become available in the near future 3.
• Other types of blood biomarkers, such as those that detect changes in amyloid-β (Aβ) structure, are also being researched and may have potential for early diagnosis of Alzheimer's disease 4.

Limitations and Future Directions

• While blood tests for Alzheimer's disease show promise, they are not yet widely used in clinical practice due to challenges such as accessibility and understanding of individual assay information and methodology 2, 5.
• Further research is needed to develop and refine blood tests for Alzheimer's disease, including the establishment of standardization and validation protocols 5, 6.
• The use of blood tests for Alzheimer's disease diagnosis is expected to continue to evolve, with the potential for earlier and more accurate diagnosis 3, 4, 6.