By Danielle Krol, MD (@dailydoseMD)

A blood test for early Alzheimer's disease may be on the horizon, according to a new small study that links substances found in blood to mental decline three years later.

Researchers at Georgetown University developed a test that looks for 10 substances in the blood known as cell membrane lipids - substances that they believe may be connected to the breakdown of certain cells in the brain. What they found was that people who had lower levels of these substances - even if they showed no signs of Alzheimer's or mild cognitive impairment - were more likely to develop mental decline within three years. The test, in fact, predicted this with more than 90 percent accuracy.

"The principle difference is we actually looked at individuals without symptoms, tracking them to see if they developed the disease," said Dr. Howard Federoff, vice president of health sciences at Georgetown University and lead author of the study published today in the journal Nature Medicine. "No other study has done this."

Federoff and his team followed 525 men and women aged 70 years and older for five years. Some of these subjects already had Alzheimer's or mild cognitive impairment, while some did not. As time passed, they took note of which subjects developed cognitive problems, and they compared those subjects' blood tests to the subjects who did not experience these changes. The comparison appeared to reveal the importance of the 10 cell membrane lipids in the development of mental decline.

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Federoff stressed that the research is still at its earliest stage, but he said it provides an entirely new framework upon which other scientists may build.

Alzheimer's experts not involved in the research were also quick to point out the preliminary nature of the findings, adding that it is far too soon for this test to be used in the clinical setting. However, they also said the findings offer hope that such a test might one day be available.

"It is interesting and exciting," said Dr. Mary Sano, director of the Alzheimer Disease Research Center at the Mount Sinai Hospital. "But more work has to be done."

Dr. Heather Snyder, director of medical and scientific operations at the Alzheimer's Association, agreed.

"It is intriguing research, but it is still too preliminary for use in the doctor's office," she said. She added, however, that the quest for a simple blood test to look for signs of early disease is a crucially important one.

ABC News' chief health and medical editor Dr. Richard Besser said the study raises hope for early intervention.

"If you talk to anyone who's involved in developing drugs for Alzheimer's disease, they'll say you have to treat somebody before the dementia even begins," he said. "This gives hope for being able to identify those people who are going to develop dementia."

Doctor's Take

The number of Americans with Alzheimer's disease and other dementias will grow as an increasing percentage of the U.S. population ages. It's estimated, in fact, that by 2025 the number of people age 65 and older with Alzheimer's disease will reach approximately 7 million - a 40 percent increase from the estimated 5.1 million currently affected.

To date, there is no single test that can show whether a person has Alzheimer's. So the finding of this study, which suggests a panel of biomarkers in a person's blood could signal early degenerative changes in neurons within the brain prior to the onset of dementia, is intriguing. Scientists may not yet have all of the answers as to what causes Alzheimer's disease, but with ongoing clinical trials, they are discovering new methods for diagnoses - and possibly even new ways to intervene.