FGF21 and hyperinsulinism: In our study, insulin infusion increased FGF21 but did not alter FGF19, FGF23, and fetuin-A in both PCOS and controls; this is in agreement with previous reports that showed a rise in serum and skeletal muscle FGF21 levels in overweight, obese, and T2D subjects following an insulin infusion, (32) and no change in FGF19 (33) and FGF23 (34) during hyperinsulinemia in healthy volunteers.