From the Guidelines

Yes, there are blood tests to diagnose Alzheimer's disease (AD) dementia.

These tests have shown acceptable performance in detecting amyloid pathology, a hallmark of AD, with some tests demonstrating high accuracy in classifying amyloid status 1.
The most promising blood biomarker measures for amyloid status include the Aβ42/Aβ40 ratio and phosphorylated tau (p-tau) species, such as p-tau181, p-tau217, and p-tau231 1.
Blood biomarker tests have unique advantages over other diagnostic modalities, such as amyloid PET and CSF tests, including being safe, acceptable to patients, and easily scalable for widespread use in clinical practice 1.

Blood biomarker tests are now widely used in AD research studies and clinical trials, and multiple tests are clinically available 1.
However, the performance of these tests varies widely, and there is a need for standardization of collection, processing, and storage procedures to ensure reproducibility and comparability across studies 1.
Blood biomarker tests can be used to support diagnosis and monitor disease progression in AD patients, but should not be used as a standalone diagnostic test 1.

Further research is needed to establish clinical thresholds and validate the use of blood biomarker tests in clinical practice 1.
The development of novel fluid biomarkers that more specifically reflect tau pathology is ongoing, and may improve the accuracy of blood biomarker tests in the future 1.

From the Research

Blood tests for Alzheimer's disease (AD) are now available for clinical use in persons with cognitive impairment, as stated in 2.
These tests, such as the amyloid-based PrecivityAD™ test, have limitations and require pre and post-test counseling, as well as appropriate clinical evaluation to ensure accurate diagnosis 2.
Phosphorylated tau blood tests are also being developed and may soon be available for clinical use, providing an opportunity for early and accurate diagnosis of AD 2.

Recent years have seen rapid progress in developing blood biomarkers for AD, including amyloid beta (Aβ) peptides, tau protein, neurofilament light chain (NfL), and glial fibrillary acidic protein (GFAP) 3.
These biomarkers have emerged as promising tools for non-invasive and cost-effective diagnosis, prognosis, and monitoring of AD progression 3.
Blood-based biomarkers may enable earlier diagnosis and aid detection and prognosis for AD, as they are vulnerable to AD pathophysiology 4.

Despite the progress, there are still challenges and limitations associated with blood biomarkers for AD, including the need for further research and validation 3, 5.
The development of novel biomarkers is needed for early diagnosis and urgent intervention before the onset of obvious phenotypes of AD 4.
The use of blood tests for AD diagnosis requires careful consideration of their limitations and the need for appropriate clinical evaluation to ensure accurate diagnosis 2, 6.