Transparency of how health and social care data is used by researchers is crucial to building public trust. We define 'data use registers' as a public record of data an organisation has shared with other individuals or organisations for the purpose of research, innovation and service evaluation, and are used by some data custodians across the United Kingdom to increase transparency of data use. They typically contain information about the type of data being shared, the purpose, date of approval and name of organisation or individual using (or receiving) the data. However, information published lacks standardisation across organisations. Registers do not yet have a consistent approach and are often incomplete, updated infrequently and not accessible to the public. In this paper, we present an empirical analysis of existing data use registers in the UK and investigate accessibility, content, format and frequency of updates across health data organisations. This analysis will inform future recommendations for a data use register standard that will be published by the UK Health Data Research Alliance.