CSF tau proteins in evaluation of patients with suspected dementia

Using commercially available ELISA kits, we evaluated the diagnostic value of CSF total tau protein (t-tau), tau phosphorylated at threonine 181 and serine 199 (p-tau 181 and p-tau 199) in early Alzheimer's disease (AD) versus healthy controls (HC) and other primary causes of dementia, such as frontotemporal dementia (FTD), vascular dementia (VaD) and dementia with Lewy-bodies (DLB). Mean CSF t-tau and CSF p-tau 181 levels were significantly elevated in AD patients compared to FTD, VaD and HC. Discrimination between AD and DLB was maximized by using p-tau 181 with a sensitivity of 91% and a specificity of 94%, whereas t-tau was optimal to separate AD from VaD with a sensitivity of 91% and specificity of 95%. P-tau 199 showed low specificity of 20-30% in distinguishing AD from other groups when sensitivity was set at 85% or greater. We concluded that p-tau 181 and t-tau represent useful biological markers for differentiating early AD from other causes of dementia.