The investigators identified polyreactive immunoglobulin G (pIgG) in adults (published in Hepatology: https://doi.org/10.1002/hep.32134) and children (in preparation). Quantification of these pIgG using a "home-made" ELISA facilitates the diagnosis of autoimmune hepatitis (AIH) as compared to non-AIH liver diseases and healthy controls. Positivity for pIgG was independent from ANA/SMA positivity and equally diagnostic for AIH even when conventional autoantibodies (ANA/SMA/SLA/LKM) were negative.

Additionally, the frequency of pIgG was lower than conventional autoantibodies (ANA, SMA) in vaccinia/drug associated severe liver injury in a retrospective multicenter study after Covid-19 vaccination (https://doi.org/10.1016/j.jhepr.2022.100605).

Aims of the study The study aims to evaluate the diagnostic capacity of pIgG to predict AIH in comparison to other liver diseases prospectively. To avoid diagnostic inaccuracy between AIH with long-term need for an immunosuppression and drug induced liver injury with autoimmune features, which can be indistinguishable from AIH at baseline and which has a very low relapse rate after a short steroid course, a follow-up after six months is obligatory for inclusion.

Therefore, the investigators will collect one serum sample from every patient (without immunosuppressive treatment) that presents to the respective hospital for evaluation of liver disease by liver biopsy within one year after initiation of the study and that provided written informed consent. Follow-up for evaluation of steroid dependency at six months after diagnosis is obligatory.

Inclusion Criteria:

• Diagnostic liver biopsy for the work-up of any liver disease
• Informed consent
• Definition of any liver disease according to current societal guidelines

Exclusion Criteria:

• No ongoing immunosuppression at the liver biopsy or prior to the liver biopsy
• Liver biopsies for the grading or staging of an already known liver disease (e.g. non-alcoholic fatty liver disease (NAFLD), Hepatitis B/D Virus Infections (HBV/HDV Infection), …)

Any patient that presents to the respective hospital for evaluation of a so far unknown-liver disease and consents is eligible if the treating physician orders a liver biopsy for the diagnostic evaluation of the liver disease. Patients are not eligible if a liver biopsy is performed for staging or grading of an already known liver disease or if the patient is treated with immunosuppressive drugs at the time of the liver biopsy.

IPD are not shared with collaborators. Data, in general, is only provided anonymized by contributing centers.