NEW YORK, Mar 23 (Reuters Health) - Testing spinal fluid for two markers linked to Alzheimer's disease may help doctors diagnose the disease at an earlier stage, researchers report.

In a new study, screening the fluid surrounding the brain and spinal cord (cerebrospinal fluid) for the markers was more than 90% accurate in identifying patients with the disease, according to the report in the March issue of the Archives of Neurology.

An easy-to-perform test for Alzheimer's disease would be an important advance, since diagnosis of the disease is currently based on physical symptoms and brain scans to rule out other causes. Diagnosing the disease can be tricky, especially in its early stages, since other illnesses or normal aging can also cause forgetfulness and other symptoms of the disease. The only way to be certain that a person has Alzheimer's is to conduct an autopsy after death.

One approach for diagnosing Alzheimer's disease that has proved promising in laboratory testing, but that has not been tested extensively in "real world" settings, is to screen cerebrospinal fluid for substances called tau and beta-amyloid protein.

Beta-amyloid proteins make up the "plaques" that accumulate in the brains of Alzheimer's patients. As the proteins clump together to form plaques in the brains of people with the disease, levels of the protein in their cerebrospinal fluid would be expected to decrease. On the other hand, levels of tau--which are thought to form "tangles" in the brains of Alzheimer's patients--are believed to be higher, reflecting degeneration in the brain.

Dr. Niels Andreasen, of Pitea River Valley Hospital in Pitea, Sweden, and colleagues tested the accuracy of the test in 241 elderly patients who were referred to a hospital with signs of cognitive impairment.

The combined screen correctly identified 94% of patients with probable Alzheimer's disease. The test was even more sensitive for people with a genetic mutation linked to the illness, correctly identifying 99% of probable cases.

Based on the findings, the researchers conclude that screening for tau and beta-amyloid "might have a role in the clinical workup of patients with cognitive impairment, especially to differentiate early Alzheimer's disease from normal aging and psychiatric disorders."

The study "is reassuring and encouraging for the future use of these (tests)," Dr. David Knopman, of the Mayo Clinic in Rochester, Minnesota, noted in an editorial that accompanies the study.

But Knopman added that the most exciting possibility is that the test may identify the disease in people who have only mild symptoms or none at all. In 1995, Knopman served as a consultant to Athena Neuroscience, a California-based company involved in developing tests for beta-amyloid protein and tau.

Dr. Bill Thies, the vice president for medical and scientific affairs at the Alzheimer's Association in Chicago, Illinois, agreed with Knopman that having a test that could detect Alzheimer's in people with few or no symptoms "would be a wonderful advance."

In an interview with Reuters Health, Thies noted that having reliable markers of the disease would also help researchers conduct clinical trials of therapies for the disease. Screens for markers could make a big difference since they "could detect changes that might not be apparent from interviews" and examinations of patients, Thies said.

But he cautioned that this type of testing is still "a long way from the clinic. For a marker to be clinically useful, it needs to be detectable in easily collected fluids such as blood and urine," he explained.

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