Embodiments of the invention provides a method for detecting one or more biomarkers derived from a body fluid, comprising performing one or more assays for the biomarkers from a sample of the body fluid, whereby the sample is previously preserved on a solid support; wherein a change in the biomarkers provides an indication of a biological event in the brain. The invention also provides related methods for identifying a person as being at risk of dementia or Alzheimer's disease, monitoring a person for the onset or progression of dementia or Alzheimer's disease, evaluating the effectiveness of a potential pharmaceutical agent.