Biomarkers are biological indicators of the presence or absence of disease. The biomarkers referred to in Alzheimer's disease testing are:
Special types of protein in the bloodstream, cerebrospinal fluid, or brain that are known to correspond to having Alzheimer's disease.
Physical changes in the brain such as shrinkage in specific areas.
Certain tests have been developed to identify these biomarkers. They use imaging techniques, blood tests, and lumbar puncture (spinal tap). These biomarker tests are currently used only for research purposes and aren't yet standardized for widespread use.
Scientists have discovered that these biomarkers appear in the body years before any dementia symptoms, such as memory loss, become noticeable. This phase is known as preclinical Alzheimer's, as opposed to clinical Alzheimer's, which means a person has dementia symptoms that are caused by Alzheimer's disease.
Researchers don't yet fully understand what the presence or absence of specific levels of biomarkers means, however, in terms of who will go on to develop symptoms, and when.