The test also showed the same markers were found in 72% of people with mild cognitive impairment, considered an early stage of the disease, and in one-third of adults who had no cognitive problems.
Researchers from Belgium analysed 114 older adults who were cognitively normal, 200 who had mild cognitive impairment and 102 who had been diagnosed with Alzheimer's. They looked for three specific biomarkers, proteins that develop in the brain when the disease is present. A later analysis looking at brain autopsies for confirmation found the test of spinal fluid markers was correct in 64 of 68 cases.
The fact that Alzheimer's was diagnosed in about one-third of people without symptoms of the disease means that the disease process is underway well before symptoms occur, the authors said.
In an editorial accompanying the paper, two U.S. experts in the disease said that cerebrospinal fluid analysis should be put into wider practice. "There is now ample evidence that these measurements have value; physicians need to formulate when and how to incorporate cerebrospinal fluid measurements into practice," they wrote.
The use of such tests will become even more important once drugs are developed to stop or slow the progression of the disease. Ideally, experts say, people could begin taking the medications before any sign of symptoms if cerebrospinal fluid markers are positive for the disease.
The study was released Monday in the Archives of Neurology.