Tau measurements in cerebrospinal fluid (CSF) are gaining acceptance as aids to 
diagnosis of Alzheimer's disease (AD) and differentiation from other dementias. 
Two ELISA assays, the INNOTEST® hTAU Ag and the INNOTEST® PHOSPHO-TAU(181P) for 
quantification of t-tau and p-tau181 respectively, have been validated to 
regulatory standards. Validation parameters were determined by repeated testing 
of human CSF pools. Specimens from Phase 2 studies of the γ-secretase inhibitor 
semagacestat and the therapeutic antibody solanezumab at baseline and following 
12-14 weeks of treatment were also tested. Estimated intra-assay CV for repeated 
testing of 3 CSF pools were ≤11.5% and RE varied between -14.1% and +6.4%. 
Inter-assay CV for t-tau was <5% and RE was within ±8%. For p-tau181, 
inter-assay CV was <9% and RE was within ±2.5%. Total CV (intra-assay plus 
inter-assay) were below 10% for both analytes. Up to 20-fold dilutional 
linearity was demonstrated for both analytes. Stability of t-tau and p-tau181 
was demonstrated in CSF during five freeze-thaw cycles at ≤-20 °C and ≤-70 °C 
and at 18-22 °C for up to 24 h. Neither semagacestat nor solanezumab interfered 
with either assay. Inter-individual t-tau and p-tau181 concentrations were 
highly variable but intra-individual variations were small. These assays are 
suitable for analysis of CSF t-tau and p-tau181 in a single laboratory 
supporting multi-center AD clinical trials. No effect of treatment with 
semagacestat or solanezumab was observed in response to three months of drug 
administration.