Table 1

Variables used to assess factors associated with switching (present on the first day of the follow-up period unless otherwise stated)

FactorDetailed information on codingCodelist (where applicable)
Age group<65, 65–74 and 75+
Indices of Multiple Deprivation (IMD)Deciles based on residential postcodeSupplied by TPP.
Sustainability and transformation partnership (STP) membershipSTP of current registered practice – modelled as a random effectSTP are NHS administrative regions made up of one or more CCGs.
Linkage to national STPs carried out by TPP.
Care/nursing home residence statusYes/noClassification supplied by TPP based on patient’s residential address at 1 February 2020 linked to CQC care home register.
Diagnosis of AFYes/no; any time prior to follow-up period
Renal functionLatest estimated Glomerular Filtration Rate (eGFR function) (<30, 30–59 and ≥60) in the 12 months to the end of the baseline period (or ‘no evidence’ for those with no creatinine recorded in this period).eGFR calculated from creatinine records.
Creatinine clearance is recommended renal function assessment for tailoring DOAC doses for individual people. Automated calculation of Creatinine Clearance (CrCl) is not yet available in OpenSAFELY, and eGFR is used as pragmatic alternative.
Recent renal function testYes/no; within last 4 months and up to the end of the study period (this conservatively allows tests slightly outside of the recommended 3-month period, and any time during the switching period). Creatinine test or:
  •  ‘451’. Renal function test.

  •  ‘XacUK’ eGFR using creatinine (calculated using Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) per 1.73 square metres.

Number of INR tests0, 1–3, 4–6 or 7+ tests during the baseline period
Length of time on warfarin*
  • <2 years (since 16 March 2018).

  • 2–≤6 years (since June 2014, date of latest National Institute of Health and Care Excellence (NICE) AF guidance).22

  • 6–<8 years (since March 2012, date of first NICE Technology Appraisal for a DOAC for AF).23

  • ≥8 years.
Previously prescribed DOACs*Yes/no; any time prior to the baseline period.
Explicitly recorded contraindicaton to DOACYes/no; any time prior to the follow-up period.
  • *The earliest actual date of an event may be missing due to incomplete patient records (eg, lost in transfer between practices), but the earliest recorded date can be used as an approximation.

  • AF, atrial fibrillation; CCGs, Clinical Commissioning Groups; DOAC, direct-acting oral anticoagulant; INR, international normalised ratio; NHS, National Health Service.