Disclosed is a method of detecting a concentration of a biomarker in a human subject having or being at risk of developing Alzheimer's disease or Mild Cognitive Impairment (MCI). Also disclosed is a process for detecting a concentration of a biomarker in a human subject having or being at risk of developing Alzheimer's disease or Mild Cognitive Impairment (MCI) comprising (a) detecting a first concentration of lipocalin-PDS/TTR complex in a blood sample or urine sample from the subject, (b) determining a second concentration of PDS/TTR complex in a blood sample or urine sample from an unaffected individual, and (c) comparing the first and second concentrations, wherein a lower first concentration as compared to the second concentration is indicative of the subject having or being at risk of developing Alzheimer's disease.