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By Domenico Praticò, MD, FCPP

In the US, currently about 6 million individuals live with a diagnosis of Alzheimer’s disease, the most common form of dementia in the elderly. Because there is no effective cure, the disease remains one of the most critical public health issues in all developed countries. Prevention and early diagnosis have been considered as primary goals in the quest for halting and delaying the onset and/or progression of Alzheimer's disease. While preventing a disease is always the best cure for it, everybody recognizes the intrinsic importance of early diagnosis not just for Alzheimer's but for any other disease. Early diagnosis allows individuals to have improved access to high-quality medical care and support services and empowers them to actively participate in decisions concerning their care.

Today, an early diagnosis for Alzheimer's disease is typically the result of a combination of brain imaging techniques, memory assessment tests and/or measurement of specific compounds (aka, “biomarker”) in the cerebral spinal fluid of an individual. The same approach has been implemented also when evaluating the risk to develop Alzheimer’s disease later in life. In both scenarios, an individual who may experience consistent memory problems or with a strong family history for the disease, would seek a doctor’s attention who would then prescribe the various tests above described and then interpret and discuss the results with the patient.

All this could probably change soon since starting this summer anyone in the USA could potentially learn about their risk to develop Alzheimer’s disease from a simple blood test independently of a doctor’s visit. In fact, Quest Diagnostics announced the availability of the AD-Detect Test for Alzheimer’s disease, a blood test that anybody above 18 years can purchase in most of the USA states.

The test will measure the blood levels of the amyloid beta (Aβ) proteins 40 and 42, which are known to accumulate in the brain of an individual with Alzheimer’s disease forming what we call “amyloid plaques”. Some evidence would suggest that a lower ratio of these 2 proteins would signal more plaques, whereas a higher ration less of them.

The new direct to consumer test is similar to the one already commercialized by the same company, the Quest’s clinical AD-Detected Amyloid beta 40/42 Ratio test, launched back in 2022 for physicians to aid in the assessment of Alzheimer’ disease risk. However, in most of these cases before ordering it the doctor would have most likely considered some important aspects in the clinical history of the patient such as cognitive tests and brain imaging scans. 

Now all this can be bypassed, and the individual can directly purchase the test, go to a Quest clinic for blood draw and later receive the results. Would this result alone sufficient to really weight the risk to develop Alzheimer’s disease? The simple answer is “no”. If the test suggests a higher risk, the individual will then need to see a physician who most likely will prescribe cognitive and brain imaging tests to confirm or deny it. 

There is no doubt that knowing that one is at higher risk for the disease could encourage him/her to adopt lifestyle changes known to be beneficial against memory decline and dementia. However, it can also be a significant source of anxiety and psychological stress. Studies have shown that patients can be seriously affected in their feelings and behavior by any test result particularly, like in this case, if the result is not certain. 

Scientists all agree that having high blood levels of Aβ proteins does not predict nor indicate the risk of developing or having currently the disease. Importantly, the new test as well as most of the other that measure these proteins in the blood has not been evaluated or approved by the Food and Drug Administration (FDA). By contrast with the source of Aβ proteins in the CSF, which is the brain, it is known that in the body Aβ protein can be produced by other sources such as the liver and blood platelets. This knowledge obviously adds a layer of complexity in the interpretation of any result from the blood test alone.

There is no doubt that the availability of a home test that could help in early diagnosis and/or risk for Alzheimer’s disease is an important milestone in our fight against the disease. However, we should be very cautious because of some key points:

• The test alone will not provide enough information to reach a diagnosis of memory problems/cognitive decline. Only a trained physician can do it. 
• The test alone will not decide whether a patient can be enrolled in clinical trials with new treatments. 
• Aβ protein is not the only “biomarker” that can predict the onset of Alzheimer’s disease, but high levels of tau protein have also been linked to it. 
• Besides Alzheimer’s disease there are other conditions like head trauma, brain tumors and depression, just to mention a few, that can manifest with memory problems, and even changes in the levels of Aβ proteins.    

, MD, is the Scott Richards North Star Charitable Foundation Chair for Alzheimer’s Research, , and Professor of Pharmacology at the 

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