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Cohort analysis of HbA1c

The Lancet has published the results of an observational retrospective cohort study that aimed to assess the relationship between HbA1c and all-cause mortality. The study is accompanied by a comment article that discusses the findings further.

The study collected data from the UK General Practice Research Database for 27,965 individuals aged 50 years and older with a diagnosis of type 2 diabetes. The data were analysed for HbA1c and all-cause mortality. A secondary analysis looked at "large-vessel disease" which was defined as any record of myocardial infarction, stroke, coronary revascularisation, carotid or peripheral arterial revascularisation or angina.

The analysis found an association between low and high mean HbA1c and increased risk of all-cause mortality and cardiac events. The lowest risks were associated with an HbA1c of 7.5% which provides some support to the current treatment targets recommended by the National Institute for Health and Clinical Excellence (NICE) for patients on more than one glucose lowering agent.

The study acknowledges the limitations of using real world observational data. Corrections were made for age, sex, smoking status, cholesterol, cardiovascular risk and general morbidity but remaining confounding factors may still bias the results. Additionally, this analysis relies on practice level data and must accept that there may be errors and omissions in the data. Finally, the accompanying article notes that observational studies cannot demonstrate cause and effect.

The authors note that their results need independent confirmation but conclude that if confirmed "diabetes guidelines might need revision to include a minimum HbA1c value".

Action: Clinicians should be aware of the continue research in this area. Clinicians should aim for the blood glucose treatment goals specified in the current NICE Guideline and resist the temptation to treat to lower levels.