title: Variability in longitudinal cerebrospinal fluid tau and phosphorylated tau measurements.
abstract: BACKGROUND
  The influence of assay variation and duration of storage on changes in cerebrospinal fluid (CSF) levels of tau and phosphorylated (P)-tau with time was evaluated in 112 patients with various neurological disorders.
  
  
  METHODS
  These patients (aged 66+/-9 years, 52% male), referred to our memory clinic, underwent two spinal taps (mean interval 19 months) and the baseline samples were assayed twice in a sandwich enzyme-linked immunosorbent assay (ELISA): once after the first spinal tap (A1) and once in a separately stored aliquot (A2) simultaneous with the follow-up sample (B).
  
  
  RESULTS
  Coefficients of variances (CVs) of tau and P-tau levels determined in repeated spinal taps (DeltaB-A2) measured in one assay (10.9% and 7.6%) were lower (p<0.01) than the CVs observed in two different (DeltaB-A1) assays (16.5% and 11.7%). The CVs of tau and P-tau measurement of one CSF sample repeated on two occasions (DeltaA1-A2) were 12.3% and 8.6%. A difference in mean P-tau level was found if the same CSF samples were repeatedly measured in two different ELISAs (A1-A2).
  
  
  CONCLUSIONS
  Longitudinal CSF tau and P-tau are best measured in one assay resulting in a lower variability compared to measurement in two different assays. The within person variability in levels of these markers currently limits the use of these ELISAs in a longitudinal clinical setting.
authors.affiliation: Neurology Department, VU University Medical Center, Alzheimer Center, Amsterdam, The Netherlands. n.verwey@vumc.nl
authors.forename: Nicolaas A
authors.initials: NA
authors.lastname: Verwey
authors.forename: Femke H
authors.initials: FH
authors.lastname: Bouwman
authors.forename: Wiesje M
authors.initials: WM
authors.lastname: van der Flier
authors.forename: Rob
authors.initials: R
authors.lastname: Veerhuis
authors.forename: Philip
authors.initials: P
authors.lastname: Scheltens
authors.forename: Marinus A
authors.initials: MA
authors.lastname: Blankenstein
mesh_terms: D000368:Aged; D003072:Cognition Disorders / Q000134:cerebrospinal fluid / Q000378:metabolism; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009422:Nervous System Diseases / Q000378:metabolism; D010766:Phosphorylation; D013048:Specimen Handling; D013997:Time Factors; D016875:tau Proteins / Q000134:cerebrospinal fluid* / Q000378:metabolism*
chemical_list: D016875:tau Proteins