GPT and hyperthyroidism: In model 3, with further adjustment with TG, TC, and hyperthyroidism, we found serum FGF21 levels remained independently associated with elevated ALT [1.42 (1.01–1.99), p < 0.043], but the significant association between serum FGF21 and elevated AST disappeared [1.23 (0.82–1.84), p < 0.318].