Methods are described in full in the paper. Briefly:
* SLE Read codes, were identified from the CPRD dictionary and from review of code lists reported in previous CPRD studies. 
* Code lists were reviewed independently by two rheumatologists  and those with agreement retained. 
* Clinical and immunological features suggestive of SLE based on the 2019 EULAR-ACR classification criteria were found. 
* Immunosuppressants were amended to include SLE related medications which are now more widely used (addition of Leflunomide, Mycophenolate Mofetil, Rituximab and Tacrolimus and Belimumab). 
* Test data (e.g. white cell count) had inclusion thresholds set based on unit types and expected normal values.