Laboratory tests

You may need lab tests to rule out other conditions that cause symptoms similar to Alzheimer's dementia. For example, you may have a thyroid test or a vitamin B-12 test.

If you have trouble with thinking and memory, your healthcare team may order blood tests to check for signs connected to Alzheimer's disease. These signs are called biomarkers.

One biomarker linked to Alzheimer's is a protein called tau, specifically p-tau217. Alzheimer's causes certain proteins to build up and form clusters in the brain. Clusters of misfolded proteins are known as amyloid plaques, and clusters of tau are known as neurofibrillary tangles.

When these Alzheimer's-related changes happen, they create high levels of p-tau217 in the blood. If your blood test shows high levels of p-tau217, it strongly suggests your cognitive decline is due to Alzheimer's disease. This test should not be done if you show no signs of cognitive decline, even if you have a family history of Alzheimer's.

Also, your cerebrospinal fluid may be tested to help diagnose Alzheimer's. Amyloid and tau proteins can be measured in the fluid. Levels of the protein abeta42 will be tested along with ratios between levels of protein. These ratios include how much abeta42 is in the fluid compared to abeta 40 and how much p-tau181 is in the fluid compared to abeta42.

Results from these tests are closely linked to Alzheimer's-related brain changes and how these changes show up on a brain-imaging test known as an amyloid-PET scan. Most of the time, a cerebrospinal fluid test is not needed for a diagnosis. But the test may be useful in some instances or if symptoms are quickly getting worse.