ß-Amyloid in Cerebrospinal Fluid: How to Keep It Floating (Not Sticking) by Standardization of Preanalytic Processes and Collection Tubes.

ABSTRACT

BACKGROUND: Phosphorylated tau (pTau), total tau (tTau), and ß-amyloid (Aß) are established cerebrospinal fluid (CSF) biomarkers used to help diagnose Alzheimer disease. Preanalytic workups of CSF samples lack harmonization, making interlaboratory comparison of these biomarkers challenging. The Aß adsorbs to sample tubes, yielding underestimated concentrations, and may result in false Alzheimer disease diagnosis. Our primary aim was to compare Aß recovery across multiple polypropylene tubes and to test the stability of tTau, pTau, and Aß in the best performing tube. METHODS: Eight polypropylene tubes were tested using 3 CSF pools with Aß concentrations <500, 500-1000, and >1000 ng/L. All samples were analyzed in duplicate. Tubes were cut open to assess their different infrared adsorption spectra. Freshly drawn CSF from 14 patients was distributed into 4 Sarstedt 5-mL (no. 63.504.027; Sar5CSF) tubes, left at room temperature for up to 7 days, and analyzed for pTau, tTau, and Aß by ELISA. RESULTS: Two Sarstedt 5-mL tubes and a Sarstedt 10-mL (Sar10CSF) tube showed significantly higher Aß recovery at all 3 concentrations compared with the 5 other tubes. The infrared adsorption spectra of Sar10CSF and Sar5CSF tubes were practically identical, unlike the other tubes. No significant loss of pTau, tTau, and Aß was observed in CSF left at room temperature for up to 7 days (P > 0.05). CONCLUSIONS: Recovery of Aß from Sar5CSF tubes is equivalent to Aß recovery from Sar10CSF tubes. Levels of pTau, tTau, and Aß were stable for at least 7 days at room temperature but not at 37 °C.