Although Alzheimer's disease is the most commonly diagnosed form of dementia, a diagnosis of one hundred percent certainty is impossible until after a person has died and autopsy can be performed. Because of the uncertainty of Alzheimer's in living patients, scientists have been racing to find a determinant biomarker for the disease. Now, a team of researchers from Saarland University, in Germany, say they have found a way to test blood for the disease.

Alzheimer's disease is an irreversible, progressive disease that affects a person's ability to remember, as well as their general thinking skills. It's so severe that it affects a person's ability to function even during the most basic tasks of daily life. In the U.S., an estimated 5.1 million people might have the disease.

MicroRNA's Role in Alzheimer's

Their test focused on microRNAs — small non-coding RNA molecules that play a role in gene expression. Because they also travel throughout the blood stream, the researchers took the blood of 48 Alzheimer's patients and 22 control participants. They found 140 mature microRNAs that were at different levels in the Alzheimer's patients than in the controls. Of these, they chose 12 as the basis for their next test, according to a Science Daily.

They then tested for these 12 microRNAs among a group of 202 participants. To see how accurate the test was, they not only included Alzheimer's patients and control participants, but also patients with mild cognitive impairment, multiple sclerosis, Parkinson's disease, depression, bipolar disorder, and schizophrenia.

They found that the test was over 95 percent accurate in differentiating between the control patients and those with other brain disorders. When they tested whether it could differentiate Alzheimer's from the rest it was 75 percent accurate. The researchers said that by using different microRNA from the previous test, they would be able to find the most accurate combination to test for Alzheimer's.

"This is an interesting approach to studying changes in blood in Alzheimer's and suggests that microRNAs could be playing a role in the disease," Dr. Eric Karran, from the charity Alzheimer's Research, told BBC. He says that the blood test might still be far away from being used in a clinical setting, at least by itself.

"A blood test to help detect Alzheimer's could be a useful addition to a doctor's diagnostic armory, but such a test must be well validated before it's considered for use," he said. "We need to see these findings confirmed in larger samples, and more work is needed to improve the test's ability to distinguish Alzheimer's from other neurological conditions."

There's Another Blood Test

This is not the first announcement of a blood test that may detect Alzheimer's though.

In May, scientists at CSIRO, Australia's national government body for scientific research, found blood-based biomarkers associated with the protein amyloid beta, which clumps together in Alzheimer's patients' brains, developing into the plaque that's believed to disrupt connections associated with memory.

Dr. Samantha Burnham, from CSIRO's Preventative Health Flagship, said this knowledge was useful because amyloid beta levels become abnormal almost 17 years before dementia symptoms start to appear, giving them a "much longer time to intervene to try to slow disease progression."

Source: Leidinger P, Backes C, Deutscher S, et al. A blood based 12-miRNA signature of Alzheimer disease patients. Genome Biology. 2013.