Variability in HbA1c associated with adverse outcomes

By Colin Kenny, Editor – Diabetes Distilled

Investigators wanted to examine whether variation in HbA_1c, the degree of variability and how HbA_1c varies over time predict hospitalisation and mortality in individuals with type 2 diabetes. They performed a retrospective analysis of a large cohort of patients from UK primary care and found that HbA_1c variability was strongly associated with overall mortality and emergency hospitalisation. This was not explained by average HbA_1c or hypoglycaemic episodes. Findings were similar for emergency hospitalisations; however, increasing average HbA_1c rather than variability was predictive of emergency hospitalisation for coronary artery disease and ischaemic stroke. Investigators suggest that clinical targets should focus on both the stability and absolute level of HbA_1c.

Most diabetes management guidelines focus on target HbA_1c levels. HbA_1c often varies over time. Long-term variability in HbA_1c may be predictive of hospitalisation or mortality, but its importance at different average levels or trajectories is unclear. In this study, investigators searched Clinical Practice Research Datalink and identified 58,832 patients with type 2 diabetes who had sufficient HbA_1c data over a 3-year period (average HbA_1c, variability and estimated trajectory) for inclusion in the study. They adjusted the resultant emergency hospitalisation and mortality hazard ratios for age, sex, smoking status, body mass index, duration of diabetes and deprivation.

Investigators discovered a consistent dose–response relationship between HbA_1c variability and mortality. Trajectory had no effect on mortality. Average HbA_1c level was important among patients who had the most unstable HbA_1c levels (the top 10%); mortality was almost twice as high as in patients with the most stable HbA_1c. Similar trends were identified for emergency hospitalisations; however, increasing average HbA_1c rather than variability was predictive of emergency hospitalisation for coronary artery disease and ischaemic stroke. Investigators concluded that HbA_1c variability was strongly associated with poor outcomes and was not explained by average HbA_1c or hypoglycaemic episodes. 
 
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