Blood Testing for Alzheimer's Disease: How Will This Affect Neuroimaging?

Alzheimer's disease (AD) is defined as amyloid plaques, tau tangles and degeneration of nerve cells in the brain leading to memory problems, cognitive decline and dementia. Currently, there are no treatments that slow the progression of AD, but a number of treatments are in late-stage clinical trials and some appear promising.

The role of brain scans

CT and MRI are able to detect brain shrinkage resulting from neurodegeneration. Hippocampal and temporoparietal atrophy is consistent with more advanced stages of Alzheimer's disease but MRI lacks both sensitivity and specificity. During the past decade amyloid PET scans and more recently tau PET scans provide molecular specificity for diagnosis. However, the high cost of PET scans, and the failure of Medicare and insurers to provide reimbursement have greatly limited the use of these diagnostic methods.

The role of blood tests

During the past two years, blood tests for amyloid, tau and neurodegeneration have been validated and demonstrated to have very high sensitivity and specificity for Alzheimer's disease diagnosis. Already one of these tests has been Clinical Laboratory Improvement Amendments (CLIA)- approved and we can expect many more to be certified. The reimbursement for such blood tests is yet to be determined, but because of their low cost, reimbursement is probably more likely than what has happened for PET scans.

If we assume that blood tests for Alzheimer's disease become available, what will be the impact on MRI and PET scanning? No one knows the answer, but there are at least two major possibilities:

1. The first is that availability of blood testing will reduce the need for MRI/PET scans for AD.
2. The second possibility is that blood testing will lead to more MRI/PET scans, because the blood tests will not be able to demonstrate regional changes in the brain which are shown on scans.

Finally, at this current time there are no treatments that work, but this could change as early as next year. Aducanumab is being reviewed by the FDA, but there are differing opinions in the scientific community regarding its effectiveness. If and when effective treatments are approved by the FDA - and hopefully reimbursed by the insurers - we can expect a huge increase in Alzheimer's disease diagnosis, both by blood tests as well as MRI and PET.