It has been a decade since the publication of white paper Shankar, et al. (2008) for immunogenicity assay cut point determination. However, the immunogenicity assay community has long been bothered by the ad hoc outlier removal criterion for assay cut point determination. In this presentation, for the first time, the inter-relationship among biological variability, analytical variability and outliers was explored. Some sensible criterion was investigated to guide outlier removal. New definition on assay sensitivity was also discussed along this line.