Alzheimer's Test That's 100 Percent Accurate? Not Yet

Researchers claimed to have identified markers for early Alzheimer's disease in some patients by analyzing results of a spinal tap, according to an article published Monday in the Archives of Neurology. Their results, they claim, are nearly 100 percent accurate in predicting Alzheimer's in some patients.

But many experts are quick to question how reliable these results may be.

"The test is an advance and has tremendous research potential. This is sure," said Karl Herrup, chair of Cell Biology and Neuroscience at Rutgers University in Piscataway, N.J.

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But, he added, "a dangerous, though unintended, consequence of the '100 percent accuracy' descriptor is that people who may not be on the fast track to Alzheimer's will end up frightened unnecessarily from a positive test result."

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"[T]he fear of [Alzheimer's disease] is so strong in our population that feeding it any way seems not in our best overall interest."

And ABC News Senior Health and Medical Editor Dr. Richard Besser said the test is not yet ready for prime time.

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"This test isn't ready to be used on healthy, normal people," Besser said on "Good Morning America."

"It will be useful for research, doing drug trials in a group of people who may be at high likelihood to go on for Alzheimer's disease."

The researchers measured tracked results from a spinal tap from three groups of patients: those with Alzheimer's, those who had been diagnosed with mild cognitive impairment (MCI), and those who were relatively healthy. Specifically, the researchers looked for patterns in the levels of two types of proteins, known as tau and amyloid, that appear to have a link to the chances of developing Alzheimer's. The data suggested that patients who had Alzheimer's or MCI had a combination of low levels of amyloid beta protein, known to form plaques in the brain, and high tau protein levels, which is known to build up dead nerve cells in the brain.

However, one-third of the study participants were identified as having levels of these proteins that suggested an Alzheimer's diagnosis -- even though they were cognitively normal. Herrup said that even if the test results are accurate, it may only mean that a patient could have a marker for the disease, but may never get the disease. He said for the moment, there is nothing a patient can do once they learn about the results of the test.

"People who take this test and are told the results are going to need a very high degree of medical sophistication in order to think about their results properly," Herrup said.

Alzheimer's Finding May Help Research, but Not Yet For Patients

While spinal fluid tests are often performed to screen for neurological infections such as meningitis or other types of brain or spinal cord damage, many experts agreed the results of this study only add to existing research for early Alzheimer's diagnosis.

In fact, out of 29 Alzheimer's disease experts who responded to a question posed by the ABC News Medical Unit, 22 said they viewed the study results as a continuation of Alzheimer's research. Only two said they could see the test as a screening method for Alzheimer's diagnosis.

"A test won't be beneficial for screening in a population if there are no current effective interventions (treatments) that can significantly affect the natural history of the condition for which one is screening, which is currently the case for Alzheimer's disease," said Dr. Ken Langa, co-director for the Center for Research and Education at the University of Michigan Health System, in an e-mail.

Dr. Clifford Saper, chairman of the department of neurology at Beth Israel Deaconess Medical Center, said until experts are able to successfully treat Alzheimer's disease, there is no reason to perform this test on patients with MCI or Alzheimer's disease.

"This test shows up positive in presymptomatic individuals, and Alzheimer's disease is a common disorder," said Saper. "The main value would be to detect [Alzheimer's disease] in atypical cases."

What the Future Holds

There are more steps to take to besides researching whether the test works, according to the coinciding editorial published in Archive of Neurology. Less experienced physicians would need to get comfortable with the idea of taking the time to prepare and perform a spinal tap. Patients and physicians would need to understand the risk involved in taking the test, and understand what the results mean.

And, according to Dr. William Hu, assistant professor of neurology at Emory University School of Medicine, the question is not whether the test works to identify potential markers for the disease, but whether those who have these markers actually develop the disease in the long run.

"The key question remains whether some the cognitively normal subjects with the [Alzheimer's disease] signature will go on to develop clinical disease, have the signature because of shared risks for [Alzheimer's disease] as those who do have the disease, or are resistant to disease despite similar changes in the brain," said Hu.

Dr. Gary Kennedy, director of the division of geriatric psychiatry at Montefiore Medical Center, said even if the test found that a higher amyloid protein may be a marker for Alzheimer's disease, there are still no successful anti-amyloid treatments available. The relevance of this marker so far is limited to confirming the diagnosis, said Kennedy.

"The real impact of these findings will be in subsequent studies of anti-amyloid drugs where spinal fluid can be used to test their immediate effects," said Kennedy. "Even so we still need to determine if lowering amyloid levels is associated with improved memory."

"We have a long way to go," he said.