The aim of our study was to clarify the association between glycated haemoglobin (HbA1c) and postoperative outcomes in people without an existing diagnosis of diabetes.

Half a million adults were recruited into the UK Biobank prospective cohort study between March 2006 and October 2010.

We divided participants into three groups: no diagnosis of diabetes and HbA1c < 42 mmol.mol−1; no diagnosis of diabetes and elevated HbA1c (≥ 42 mmol.mol−1 with no upper limit); and prevalent diabetes (regardless of HbA1c concentration) at recruitment.

We followed up participants by linkage with routinely collected hospital data to determine any surgical procedures undertaken after recruitment and the associated postoperative outcomes.