Variability in the Laboratory Measurement of Cytokines A Longitudinal Summary of a College of American Pathologists Proficiency Testing Survey

Context.-The measurement of cytokines in clinical laboratories is becoming an increasingly routine part of immune monitoring when administering biologic and cell-based immunotherapies and also for clinical assessment of inflammatory conditions. While a number of commercial assays and platforms are available for cytokine measurement, there is currently little standardization among these analytical methods. Objective.-To characterize the variability and comparability among cytokine testing platforms that are commonly used in clinical laboratories. Design.-We analyzed data for 4 cytokines (interleukin [IL]-1, IL-6, IL-8, and tumor necrosis factor-alpha [TNF-alpha]) from 6 College of American Pathologists cytokine surveys administered from 2015 to 2018. Analyses interrogated variability between testing methods and variability within each laboratory across the mailings. Results.-Significant variability was noted across methods with analysis of IL-1 showing the least variability and IL-6, IL-8, and TNF-alpha varying between methods to a greater extent. Intralab variability was also significant with TNF-alpha measurements again showing the greatest variability. Conclusions.-This retrospective analysis of College of American Pathologists proficiency testing data for cytokine measurement is the largest method comparison to date, and this study provides a description of the variation of cytokine measurement across methods, across laboratories, and within laboratories. Serial monitoring of cytokines should preferentially be performed by the same method within the same laboratory.