FGF21 and autoimmune hepatitis: Our research did not also show statistically significant differences in the concentration of FGF21 depending on age and the period of blood collection, with two exceptions (a higher concentration of FGF21 before transplantation in the group under 45 years of age in PBC patients; a lower concentration of FGF21 before transplantation in the group under 45 years of age in AIH patients).