Edward C. Geehr, M.D.

Alzheimer's disease has a huge impact on patients and families. Wouldn't a diagnostic blood test be helpful?

Alzheimer's disease is a progressive condition that kills off brain cells and inexorably leads to dementia, physical decline and death. Today, an American develops Alzheimer's disease every 68 seconds. There is no known cure. Research into possible treatments is hampered by the absence of a reliable, cost-effective test that can predict future onset of the disease.

A research letter published in the journal Nature Medicine describes a new blood test that predicts with 90% accuracy the onset of cognitive impairment, or Alzheimer's, in the next two to three years. The researchers from the University of Rochester, Georgetown University and the University of California, Irvine identified 10 different blood lipids that were depleted in patients who later became impaired.

Discovery of a sensitive and reliable test could vastly expand the number of research protocols focused on preventing the progression of the disease in those known to be at high risk. Prevention is important with Alzheimer's, because once the diagnosis is established clinically the brain damage is already extensive. Best to detect it early.

In order to identify possible blood markers for the disease, researchers recruited 525 subjects who were at least age 70, and collected blood samples for extensive testing. Forty-six subjects were diagnosed with Alzheimer's when entering the study and another 28 developed the disease over the course of the next five years, for a total of 74.

Researchers then compared the blood of 53 of the 74 subjects with those of 53 other matched control subjects without signs of the disease. A comparison of blood profiles between those groups led to the discovery of the 10 lipid markers thought to result from the breakdown in nerve-cell membranes.

In order to validate the lipid markers, 21 of the remaining group of 74 subjects with Alzheimer's were matched with an additional 20 control subjects from the original 525 study recruits. Blood samples were blinded, or anonymous, as researchers attempted to predict the presence of Alzheimer's on the basis of the 10-lipid panel. They were able to predict those who had the disease with 90% accuracy.

Further testing will be required to validate the results; the implications are significant. For example, are certain ethnic groups more or less likely to produce similar results? Will the predictive accuracy hold up when greater numbers are tested?

As a humanitarian and scientific issue, testing accuracy is critical. For example, false positive tests might incorrectly predict the future onset of the disease and needlessly alarm an individual and family about a devastating illness they will never get. Or a false negative result might incorrectly assure people that they don't have to prepare themselves for the oncoming ravages of the disease.

But finding a valid test is imperative. The number of Americans with Alzheimer's is expected to rise along with the aging of the population. By 2025, the number of Alzheimer's patients is expected to increase by 40%, from about 5 million in 2013 to greater than 7 million.

Alzheimer's is the 6^th-leading cause of death in the U.S. overall, and the 5^th-leading cause for those ages 65 and older. Death from Alzheimer's increased 68% between 2000 and 2010.

For those who are concerned about whether they or a loved one might have the disease, an initial evaluation by your primary care physician is useful to help rule out other, common and sometimes reversible causes of early-onset dementia. Further evaluation by a neurologist along with some additional testing can help confirm the diagnosis. While there is no cure, measures to prepare the home and create a plan for caregivers are best undertaken before the dementia becomes severe.