Fully automated immunoassays for measuring beta‐amyloid peptide (1‐42) and total tau in cerebral spinal fluid

AbstractBackgroundBeta‐amyloid1‐42 (Aβ42) and tau protein are cerebral spinal fluid (CSF) biomarkers for progression to AD. The sensitivity requirements for Aβ42 and total tau assays are in the pg/mL range, a challenge for any methodology. The use of these biomarkers for clinical purposes requires assays that can reliably deliver accurate and reproducible results.MethodNew prototype immunoassays for Aβ42 and total tau on a fully automated clinical analyzer [Siemens Healthineers ADVIA Centaur® XPT Immunoassay System] are under development to enable routine testing of AD biomarkers in clinical laboratories. Each assay uses an antigen/antibody sandwich format and chemiluminescence detection. Standard curves from 0 to 4000 pg/mL and 0 to 6500 pg/mL were generated for the Aβ42 and Tau assays, respectively. Synthetic Aβ42 and recombinant tau‐441 were spiked into an immunodepleted (ID) CSF pool and tested. Precision was evaluated over 6 days by testing a CSF pool and buffer controls on two analyzers. Functional sensitivity was estimated using the precision data. Clinical utility was evaluated by testing 30 clinical CSF samples from subjects with and without AD.ResultRecoveries of spiked Aβ42 from CSF ranged from ‐13% to +0.7% over 113 to 3179 pg/mL. Recoveries of spiked tau‐441 from CSF ranged from ‐11% to +13% over 35 to 3826 pg/mL. The repeatability and within‐laboratory precision of the Aβ42 assay ranged from 1.3% to 8.6% and 1.9% to 9.9%, respectively, over 107 to 2005 pg/mL. The repeatability and within‐laboratory precision of the total tau assay ranged from 1.2% to 10.8% and 1.6% to 12.5%, respectively, over 108 to 3300 pg/mL. The functional sensitivities of the Aβ42 and total tau assays were estimated to be < 200 pg/mL and < 80 pg/mL, respectively. Using ROC analysis, a ratio of Aβ42 and total tau results was able to differentiate AD from non‐AD subjects with 90% sensitivity and 95% specificity (AUC 0.95).ConclusionWhen finalized, the fully automated Aβ42 and total tau assays will have performance characteristics suitable for routine use in a clinical laboratory. The performance of the assays in combination with automation will make testing for these important biomarkers more reliable and routine.