This document provides interim guidance to countries on testing considerations and strategies for suspect cases of severe acute hepatitis of unknown aetiology in children. It is primarily intended for clinical, programmatic, laboratory and diagnostic stakeholders across Member States and national public health authorities involved in the identification and investigation of cases of severe acute hepatitis in children. This document is part of a package of guidance for this event, which includes suggested minimum reporting variables and a clinical Case Report Form support Member States with case investigation and reporting.