Early detection strategies are focused on identifying either the earliest pathological expression of a disease before there are clinical signs, or to detect the first clinical signs of a disease. Screening tests can be conducted without the full clinical presentation of a disease. In some cases, surrogate markers can be employed for early detection when their presence is clearly associated with a disease. An example of a surrogate marker is high cholesterol for early detection of heart disease. In Alzheimer's disease, we may be able to detect the disease in the brain years before there is cognitive loss, for example, by neuroimaging. Early detection affords the possibility of using drugs and lifestyle interventions to prevent or slow the detection of a disease in its earliest stages.