CSF biomarker variability in the Alzheimer's Association quality control program

Abstract

Background The cerebrospinal fluid (CSF) biomarkers amyloid beta 1–42, total tau, and phosphorylated tau are used increasingly for Alzheimer’s disease (AD) research and patient management. However, there are large variations in biomarker measurements among and within laboratories. Methods Data from the first nine rounds of the Alzheimer’s Association quality control program was used to define the extent and sources of analytical variability. In each round, three CSF samples prepared at the Clinical Neurochemistry Laboratory (Mölndal, Sweden) were analyzed by single-analyte enzyme-linked immunosorbent assay (ELISA), a multiplexing xMAP assay, or an immunoassay with electrochemoluminescence detection. Results A total of 84 laboratories participated. Coefficients of variation (CVs) between laboratories were around 20% to 30%; within-run CVs, less than 5% to 10%; and longitudinal within-laboratory CVs, 5% to 19%. Interestingly, longitudinal within-laboratory CV differed between biomarkers at individual laboratories, suggesting that a component of it was assay dependent. Variability between kit lots and between laboratories both had a major influence on amyloid beta 1–42 measurements, but for total tau and phosphorylated tau, between-kit lot effects were much less than between-laboratory effects. Despite the measurement variability, the between-laboratory consistency in classification of samples (using prehoc-derived cutoffs for AD) was high (>90% in 15 of 18 samples for ELISA and in 12 of 18 samples for xMAP). Conclusions The overall variability remains too high to allow assignment of universal biomarker cutoff values for a specific intended use. Each laboratory must ensure longitudinal stability in its measurements and use internally qualified cutoff levels. Further standardization of laboratory procedures and improvement of kit performance will likely increase the usefulness of CSF AD biomarkers for researchers and clinicians.

Importance and Impact of Preanalytical Variables on Alzheimer Disease Biomarker Concentrations in Cerebrospinal Fluid

“…Moreover, no significant changes in A␤ arose from the addition of 5000 lysed erythrocytes/mm 3 (6 ). The concentrations of A␤ and T-tau were also determined in 1 severely blood-contaminated sample (28.800 erythrocytes/mm 3 ) that had been divided, with 1 aliquot being centrifuged before freezing and 1 aliquot not centrifuged, which did not lead to a considerable difference (11 ). The present data, combined with the majority of the data from the literature, allows us to conclude that centrifugation (before or after freezing) does not affect CSF biomarker concentrations, probably not even when CSF is contaminated with blood.…”

Perspective on future role of biological markers in clinical therapy trials of Alzheimer's disease: A long-range point of view beyond 2020

“…To date, the major cause of the experimental variability for CSF biomarkers is due to between-laboratory factors [107]. Since global biomarker cut-off levels cannot be defined owing to the high extent of variability, each laboratory should employ internally validated cut-off values and guarantee longitudinal stability in its measurements.…”

“…Since global biomarker cut-off levels cannot be defined owing to the high extent of variability, each laboratory should employ internally validated cut-off values and guarantee longitudinal stability in its measurements. Progresses in standardization of laboratory protocols in conjunction with the enhancement of kit performance and the use of fully automated tools are expected to improve the effectiveness of CSF AD biomarkers for both researchers and clinicians [107].…”

“…The authors report that the body of evidence for these imaging and CSF biomarkers is still limited and variable across the different types of biomarkers [310]. As far as the CSF biomarkers are concerned, it was recently reported that the overall variability of data coming from a total of 84 laboratories remains too high to allow the validation of universal biomarker cut-off values for the specific intended use [107], which underscores the urgent need for better harmonization and standardization of these methods.…”

Quantitative detection of amyloid-β peptides by mass spectrometry: state of the art and clinical applications

“…Unauthenticated Download Date | 5/11/18 7:30 PM tend to bind to other proteins in vivo [24] and they also adsorb in a non-specific manner to the plastic of collection and assay tubes [25] rendering more complex their accurate quantification. The particular physicochemical properties of Aβ peptides require therefore to control and standardize pre-analytical and analytical phases to obtain reliable measurements with both MS and ELISA, and to eventually deliver reliable results to patients [26][27][28].…”