Indeed, ex vivo colchicine challenge of undiluted whole blood showed a clear segregation of both the IL-1β and IL-18 ratios for FMF patients with classical MEFV mutations and healthy donors (figure 4 and online supplementary table 4), establishing that the functional assay can be conveniently performed on fresh blood, bypassing the need for PBMC isolation. Here, IL18 is linked to familial Mediterranean fever.