The present disclosure relates generally to the field of immunological-based diagnostic assays. Particularly, a method is contemplated herein for measuring cell-mediated immune response reactivity. The present disclosure further provides a method to reduce incidence of non-specific immune response reactivity in a cell-mediated immune response-based assay, comprising contacting a sample with a basic peptide structure capable of binding to lipopolysaccharides, such as polymyxin B or a sushi peptide.