GDF15 and immunoglobulin G4-related sclerosing disease: First, although the serum concentration of GDF-15 was correlated with some organ involvements of IgG4-RD, we observed that the conventional serum markers, including IgG4, complements, and sIL-2R, were correlated with the IgG4-RD RI score or the number of organ involvements better than GDF-15 or CCL2.