Spinal cord fluid might someday help doctors diagnose Alzheimer's disease, a preliminary study suggests.

An experimental test distinguished 15 samples from patients with Alzheimer's or a related condition from 19 non-Alzheimer's samples, researchers from Heinrich Heine University in Duesseldorf, Germany, reported in the July issue of the journal Nature Medicine.But the scientists and other Alzheimer's experts warned that it is too soon to tell how useful the test might be for doctors, who are now about 80 percent to 90 percent accurate in diagnosing the disease.

Currently there is no single diagnostic test for Alzheimer's; doctors largely rely on symptoms, psychological testing, and medical testing to rule out other diseases. The diagnosis is generally confirmed only after death by examining brain tissue.

The brains of Alzheimer patients show extensive deposits of a substance called amyloid beta-protein. The new test is designed to detect that substance in the fluid that bathes the brain and spinal cord.

Researchers have to study the test's accuracy in many more people and see if it is fooled by other diseases, experts said.