Several CSF biomarkers are used to support the diagnosis of Alzheimer's disease. Tests that may be available include amyloid β(Aβ)-42, Aβ-40, total tau (t-tau) and phosphorylated tau at position 181 (p-tau181). As amyloid plaques form, Aβ-42 levels decrease potentially due to sequestration of the protein into plaques. Shortly after amyloid plaques form, t-tau and p-tau181 levels increase. The pattern of low Aβ-42, high t-tau and high p-tau181 is associated with Alzheimer's disease pathology. Measurements of these substances are most readily interpreted as ratios (Aβ42/Aβ40, t-tau/Aβ-42, p-tau181/Aβ-42). It should be noted that these biomarkers have been studied primarily in white non-Hispanic populations.