New guidelines for the diagnosis of Alzheimer's disease are to be released today by the National Institute on Aging and the Alzheimer's Association, reports The New York Times. The new definition breaks the disease down into three stages: when dementia has set in, when there are symptoms, but the person can still perform daily tasks, and when there are not yet symptoms, but changes are occurring in the person's brain. That early, symptom-free stage would be assessed through biomarkers. The Times does note that use of biomarkers to diagnose Alzheimer's isn't yet recommended for widespread use, just for clinical trials. Scientists don't yet know "what measure is truly abnormal and what measure is not," says Marilyn Albert, from the Johns Hopkins Alzheimer's Disease Research Center, and who helped developed the new guidelines. A bill has also been proposed in the US to create Medicare cost codes for an Alzheimer's diagnosis, before it develops into dementia.