Associations between usual glycated haemoglobin and cardiovascular disease in patients with type 2 diabetes mellitus: A 10‐year diabetes cohort study

Abstract

Aim: To investigate the assocation between glycated haemoglobin (HbA1c) level and cardiovascular disease (CVD) risk among patients with type 2 diabetes.

Materials and methods: This retrospective cohort study conducted in Hong Kong selected patients aged 45 to 84 years with type 2 diabetes mellitus and without CVD from primary care clinics during the period 2008 to 2010. Usual HbA1c measurement was calculated using a mixed‐effects model to minimize regression dilution bias. The association between usual HbA1c and CVD risk was assessed by Cox regression, with adjustment for baseline covariates. Subgroup analyses by patient characteristics were also conducted.

Results: After a median follow‐up period of 8.4 years (1.4 million person‐years), 174 028 patients with 34 074 CVD events were observed. A curvilinear association was found between usual HbA1c and total CVD, stroke, heart failure and CVD mortality risk. No significant difference was found among patients with usual HbA1c <53 mmol/mol (7%). A positive linear association was found between usual HbA1c and the risks of outcomes when the usual HbA1c was 53 mmol/mol (7%) or above. The adjusted hazard ratios (HRs) for CVD risk per 1% increment in usual HbA1c >7% was 21% (HR 1.21, 95% confidence interval [CI] 1.18–1.23) (HR for CVD per 1mmol/mol increment in usual HbA1c > 53 mmol/mol was 1.7% (HR 1.017, CI 1.015‐1.019)). A similar pattern was identified in a patient subgroup analysis, but the effects of usual HbA1c in younger patients were more prominent than in older patients.

Conclusions: Usual HbA1c increments for levels >53 mmol/mol (7.0%) were associated with elevated CVD risk, but no difference was found in the population with usual HbA1c <53 mmol/mol (7.0%), irrespective of patient characteristics. For CVD prevention, strict adherence to an HbA1c target of <53 mmol/mol (7%) should apply to younger patients.