Alzheimer's biology
Blood tests for Alzheimer's disease
Is Alzheimer's-related amyloid pathology likely to be present?
A blood test for biology, not a memory test
Newer blood tests can measure proteins associated with Alzheimer's-related changes in the brain. Depending on the test, these may include phosphorylated tau, amyloid-related markers, or a combination of the two. A standard blood sample is sent to a laboratory, and the result may be reported as positive, negative, or intermediate.
These tests do not measure memory or day-to-day function. They help estimate whether Alzheimer's-related amyloid pathology is likely to be present. The specific assay matters. Different tests measure different proteins, use different thresholds, and are not interchangeable.
What the result adds
In a person who already has cognitive symptoms and has completed a clinical evaluation, a high-performing blood biomarker may make Alzheimer's disease more or less likely. The result may help determine whether PET imaging or spinal-fluid testing is still needed. It may also be part of confirming eligibility for an Alzheimer's treatment that requires evidence of amyloid pathology.
A positive result does not explain every symptom or exclude another brain disease. A negative result does not answer every diagnostic question. False-positive, false-negative, and intermediate results occur, and more than one condition may be contributing to a person's difficulties.
From Dr. Anil
Why I may recommend it
I may use a blood biomarker when the result can clarify whether Alzheimer's biology is contributing to a person's symptoms and guide the next step in the evaluation. These tests are not intended to screen people without symptoms or to provide a stand-alone diagnosis.
Because this field is changing quickly, the name of the test, the laboratory, and the clinical setting all matter. The result should be interpreted as part of the full evaluation, not read in isolation from a patient portal.
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Last reviewed September 2026 by Anil R. Wadhwani, MD, PhD.