FGF21 and diabetes mellitus: In the group of patients after kidney transplantation without diabetes, a positive correlation was found between the plasma concentration of FGF21 and the serum concentration of triglycerides (R = 0.422; p < 0.001), plasma insulin (R = 0.172; p < 0.05), plasma concentration of interleukin 6 (R = 0.171; p < 0.05), and serum cystatin C concentration (R = 0.254; p < 0.005).