The UK Cystic Fibrosis Registry Sweat Chloride Tests is made up of data items relating to sweat chloride tests taken during CF patients encounters at NHS hospitals in UK. The UK CF Registry is a centralised database of all 60 CF centres across the UK. Data are manually entered in calendar years by CF clinical teams for the 99% of people with a diagnosis of CF who consent to their data being donated to the Registry. Data are entered onto a secure web-portal. Sweat tests refer to sweat chloride tests taken by CF patients in relation to diagnosis of CF, investigations or as part of protocol for initiating onto CFTR modifier drug treatments. For more information please see www.cysticfibrosis.org.uk/registry and 'Data Resource Profile: The UK CF Registry' published in the International Journal of Epidemiology (2018 Feb 1;47(1)9-10e).