Alzheimer’s disease CSF biomarker assays: Impact of methodology changes in clinical practice

Abstract Background Decreased amyloid β 1‐42 (Aβ42) and increased tau (t‐Tau p‐Tau) concentrations in cerebrospinal fluid (CSF) reflect the pathological changes of Alzheimer’s disease (AD) aid diagnosis AD dementia. In United States, ADmark® assay has been almost exclusively used for measurement these biomarkers clinical practice. Recently, our institution switched from to Roche Elecsys assays. The goal this study was determine if differences exist between methods classification patients as having indicative pathology. Method Patients undergoing ADMark® testing (n= 73) were recruited participate IRB‐approved study. Two simultaneous CSF aliquots obtained. For ADMark®, 2.0mL collected into a 5mL polypropylene (PP) tube shipped frozen Athena Diagnostics per collection instructions (Innotest® immunoassays Aβ42, t‐Tau, p‐Tau). assays (Aβ42, p‐Tau), 2.5mL low bind PP tube, frozen, then tested at Mayo Clinic Laboratories. Comparative analysis performed two methodologies findings. Result Overall concordance Aβ42/t‐Tau index (ATI) p‐Tau/Aβ42 89% with 8 (11%) discrepant cases. Four cases classified normal by but borderline (n=3) or abnormal (n=1) ATI. cases, result most consistent diagnosis. When compared diagnosis, suspicion dementia 84% 92% ATI p‐Tau/Aβ42, respectively. without dementia, results 19% 21% There 2 5 that Conclusion showed comparable performance when correlating