Effects of processing and storage conditions on amyloid beta (1-42) and tau concentrations in cerebrospinal fluid: Implications for use in clinical practice

Background: Reported concentrations of amyloid beta (1-42) (Abeta42) and tau in cerebrospinal fluid (CSF) differ among reports. We investigated the effects of storage temperature, repeated freeze/thaw cycles, and centrifugation on the concentrations of Abeta42 and tau in CSF. Methods: Stability of samples stored at -80 degreesC was determined by use of an accelerated stability testing protocol according to the Arrhenius equation. Abeta42 and tau concentrations were measured in CSF samples stored at 4, 18, 37, and -80 degreesC. Relative CSF concentrations (%) of the biomarkers after one freeze/thaw cycle were compared with those after two, three, four, five, and six freeze/thaw cycles. In addition, relative Abeta42 and tau concentrations in samples not centrifuged were compared with samples centrifuged after 1, 4, 48, and 72 h. Results: Abeta42 and tau concentrations were stable in CSF when stored for a long period at -80 degreesC. CSF Abeta42 decreased by 20% during the first 2 days at 4, 18, and 37 degreesC compared with -80 degreesC. CSF tau decreased after storage for 12 days at 37 degreesC. After three freeze/thaw cycles, CSF Abeta42 decreased 20%. CSF tau was stable during six freeze/thaw cycles. Centrifugation did not influence the biomarker concentrations. Conclusions: Repeated freeze/thaw cycles and storage at 4, 18, and 37 degreesC influence the quantitative result of the Abeta42 test. Preferably, samples should be stored at -80 degreesC immediately after collection. (C) 2005 American Association for Clinical Chemistry.