Sources of Variability in Luminex Bead-based Cytokine Assays: Evidence from Twelve Years of Multi-site Proficiency Testing

Bead array assays, such as those sold by Luminex, BD Biosciences, Sartorius, Abcam and other companies, are a well-established platform for multiplexed quantification of cytokines and other biomarkers in both clinical and discovery research environments. In 2011, the National Institute of Allergy and Infectious Diseases (NIAID)-funded External Quality Assurance Program Oversight Laboratory (EQAPOL) established a proficiency assessment program to monitor participating laboratories performing multiplex cytokine measurements using Luminex bead array technology. During every assessment cycle, each site was sent an assay kit, a protocol, and blinded samples of human sera spiked with recombinant cytokines. Site results were then evaluated for performance relative to peer laboratories. After over a decade of biannual assessments, the cumulative dataset contained over 15,500 bead array observations collected at more than forty laboratories in twelve countries. These data were evaluated alongside post-assessment survey results to empirically test factors that may contribute to variability and accuracy in Luminex bead-based cytokine assays. Bead material, individual technical ability, analyte, analyte concentration, and assay kit vendor were identified as significant contributors to assay performance. In contrast, the bead reader instrument model and the use of automated plate washers were found not to contribute to variability or accuracy, and sample results were found to be highly-consistent between assay kit-manufacturing lots and over time. In addition to these statistical analyses, subjective evaluations identified technical ability, instrument failure, protocol adherence, and data transcription errors as the most common causes of poor performance in the proficiency program. The findings from the EQAPOL multiplex program were then used to develop recommended best practices for bead array monitoring of human cytokines. These included collecting samples to assay as a single batch, centralizing analysis, participating in a quality assurance program, and testing samples using paramagnetic-bead kits from a single manufacturer using a standardized protocol.