Variability in longitudinal cerebrospinal fluid tau and phosphorylated tau measurements.
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.
Verwey
Nicolaas A
NA
Neurology Department, VU University Medical Center, Alzheimer Center, Amsterdam, The Netherlands. n.verwey@vumc.nl
Bouwman
Femke H
FH
van der Flier
Wiesje M
WM
Veerhuis
Rob
R
Scheltens
Philip
P
Blankenstein
Marinus A
MA
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*
D016875:tau Proteins