Beta-Amyloid In Cerebrospinal Fluid: How To Keep It Floating (Not Sticking) By Standardization Of Preanalytic Processes And Collection Tubes

Background: Phosphorylated tau (pTau), total tau (tTau), and beta-amyloid (A beta) 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 A beta adsorbs to sample tubes, yielding underestimated concentrations, and may result in false Alzheimer disease diagnosis. Our primary aim was to compare A beta recovery across multiple polypropylene tubes and to test the stability of tTau, pTau, and A beta in the best performing tube.Methods: Eight polypropylene tubes were tested using 3 CSF pools with A beta concentrations <500, 500-1000, and >1000ng/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 7days, and analyzed for pTau, tTau, and A beta by ELISA.Results: Two Sarstedt 5-mL tubes and a Sarstedt 10-mL (Sar10CSF) tube showed significantly higher A beta 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 A beta was observed in CSF left at room temperature for up to 7days (P > 0.05).Conclusions: Recovery of A beta from Sar5CSF tubes is equivalent to A beta recovery from Sar10CSF tubes. Levels of pTau, tTau, and A beta were stable for at least 7days at room temperature but not at 37 degrees C.