The health industry is a data-intensive domain. Sharing medical data between medical facilities is necessary for providing good healthcare as well as for research in the healthcare domain. However, due to the sensitive and personal nature of health data, challenges arise when sharing this data. Consent management is a key aspect. The use of blockchain technology can enable patients to be the owner of their data, and allow them to manage who is able to view and process their data. In this paper, we define the requirements for an adequate consent management system for blockchain-based medical data sharing. After that, we compare the related work and identify limitations based on the requirements. Finally, we provide a highly dynamic consent management system with fine-grained access control using hierarchical structures, based on the Hyperledger Fabric permissioned blockchain. The proposed solution complies with the EU General Data Protection Regulation and addresses important privacy issues.