PPGL patients with diabetes showed higher levels of FGF21 than those with normal glucose tolerance (NGT) (438.2 (337) pg/mL vs. 154.5 (97) pg/mL; p = 0.007) or those with prediabetes (438.2 (337) pg/mL vs. 154.5 (97) pg/mL; p = 0.022). Here, FGF21 is linked to diabetes mellitus.