Blood Test for Alzheimer’s Disease

Test will primarily help recruit subjects for clinical trials of new drugs

There has been a flurry of interest in the news about a “new blood test for Alzheimer’s disease”. This follows a report from the same research group who excited interest last year and who we wrote a news item about at that time. This recent report extends the earlier findings and shows that a blood test for the ratio of two beta-amyloid fragments correlates well with the results of a much more complex and expensive test for brain amyloid levels; the amyloid-PET scan test.

However, the conclusions we drew at that time still apply. What is the significance of this new test? The immediate potential for the new test is going to be for clinical trials. Scientists in drug companies and universities are looking for drugs that can delay or prevent the development of Alzheimer’s disease. It is very likely that any drugs found will be most effective if used in the very earliest stages of the disease before the brain accumulates too much damage. Thus, researchers want to recruit people with no symptoms at all or those with the very earliest stages of the disease. Currently such people can only be found by using the expensive or invasive PET and spinal fluid tests. Having a blood test will make it feasible to more easily recruit volunteers for clinical trials.

What about using the test to find out if I am developing or going to develop Alzheimer’s disease? There are some problems here. Firstly, the test has not been validated for this use yet. It has mainly been tested in people with no cognitive impairment and this is a different population from those with mild cognitive impairment who are seeing their doctors for assessment. It is also true that not all people with brain amyloidosis (which this test predicts) will develop dementia. Only after larger prospective studies following people over many years will we be able to evaluate how accurately the test can predict whether any individual is going to develop Alzheimer’s disease. A final problem is that currently there are no effective strategies or treatments to prevent or treat Alzheimer’s disease. So, if a person gets a positive result on the test, they will know the potentially bad news but also know that there is nothing really effective that they can do about it.

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