Abstract: Objective To analyze the levels of thiopurine metabolites in autoimmune hepatitis (AIH) patients and their predictive value for treatment efficacy. Methods Fifty-two AIH patients were enrolled between January 2022 and December 2024 and treated with prednisone combined with azathioprine. Fifty healthy individuals undergoing routine physical examinations during the same period were enrolled as control group. Clinical parameters of AIH group and control group were compared before and after treatment. Changes in 6-thioguanine nucleotides (6-TGNs) and 6-methylmercaptopurine nucleotides (6-MMPNs) levels were analyzed across different treatment response groups, and their predictive efficacy for AIH treatment response was evaluated. Results Before treatment, AIH patients showed significantly higher levels of ALT, AST, IgG, IgM, and gamma-globulin than controls (P<0.05). After treatment, these parameters decreased significantly in AIH patients (P<0.05). At the end of treatment, 31 patients achieved complete response, while 21 had incomplete response. The 6-TGN level in the complete response group [225 (74-717) pmol/8×10⁸ RBC] was significantly higher than in the incomplete response group [150 (53,370) pmol/8×10⁸ RBC, P<0.05], whereas 6-MMPN levels did not differ significantly between groups (P>0.05). Among complete responders, 12, 10, and 9 patients achieved response within <3 months, 3~6 months, and >6 months, respectively. Rapid responders (<6 months) had significantly higher 6-TGN levels than delayed responders (>6 months) (P<0.05), while 6-MMPN levels showed no significant differences across response timelines (P>0.05). 6-TGN demonstrated strong predictive value for treatment response (AUC=0.79; diagnostic cutoff: 174 pmol/8×10⁸ RBC). Conclusion 6-TGN is a core predictor of thiopurine treatment response in AIH. A concentration >174 pmol/8×10⁸ RBCs may serve as a biomarker for complete response.

Key words: Autoimmune hepatitis, Azathioprine, 6-thioguanine nucleotides, Treatment response