For Alzheimer’s disease, a new testing solution can aid early diagnosis

There is no cure for Alzheimer’s disease (AD), and no treatment yet that can slow its course. But plasma-based diagnostic testing can help the physician confirm or exclude the diagnosis, a key step in developing an individualized treatment plan. And exercise has proven to be a powerful deterrent to age-related cognitive decline. These were just 2 of the discussion points in a recent Diagnostics Dialogues podcast with Michael Racke, MD, medical director for neurology at Quest Diagnostics.

Neurologists are used to making the diagnosis of AD after carefully considering the patient’s history (and often a report from a family member) and results of cognitive testing, and ruling out multiple other potentially treatable causes, including vitamin B12 deficiency, hypothyroidism, and depression. Other forms of dementia, including Lewy body dementia and vascular dementia, must also be considered in the differential diagnosis.

Type II diabetes and insulin resistance can increase the risk for neurodegeneration, Dr Racke points out, “and so by treating those disorders, you're often helping to slow down the neurodegeneration process.” Multiple studies have also shown that exercise is associated with slower cognitive decline, he adds, “and more intense physical activity appears to benefit patients more in terms of maintaining cognitive function.” Exercise benefits are seen not just in AD, but in other neurodegenerative diseases as well.

While there are not yet definitive treatments for AD, there is still value in confirming or ruling out the diagnosis through testing. Because there are specific treatments for B12 deficiency, hypothyroidism, and depression, as well as contributing disorders such as diabetes, “it's very important to be able to make an accurate diagnosis,” Dr Racke says, but the clinical exam is often not sufficient. “Even experts in dementia have a difficulty in identifying exactly what disorder the patient has.”

This is where Quest’s AD-Detect^TM may offer some value, Dr Racke explains. The test, performed on a simple plasma sample, measures the ratio of 2 critical fragments of amyloid-beta, called Aβ42 and Aβ40. In AD, that ratio declines over time; as the brain forms amyloid plaques, less Aβ42 reaches the bloodstream. As amyloid builds up in the brain, researchers believe, it begins to interfere with cognitive function. Establishing a baseline value of Aβ42 can aid in monitoring patients over time, and testing may help identify patients who are candidates for early treatment with antibodies or other therapies as they become available. Quest was the first commercial testing laboratory to offer this important test. 

Prior to the advent of blood testing for amyloid-beta, the only way to detect the buildup of brain amyloid was either with neuroimaging or cerebrospinal fluid (CSF) testing. 

Quest offers a CSF test, ADMark®, which measures another key AD-related protein, phospho-tau 181, along with total tau and Aβ42 for a comprehensive biomarker panel that correlates with risk of AD.

“If the patient doesn’t have biomarkers that are indicative of a neurodegenerative disorder, their cognitive decline may be due to may be due to other causes, and the physician may be able to offer more definitive treatment,” Dr Racke says.