Relationship between HbA1c and risk of all-cause hospital admissions among people with Type 2 diabetes

Aim: To investigate the relationship between HbA1c and the 2-year risk of hospitalization among people with Type 2 diabetes. Methods: In total, 4704 patients from 18 general practices in Cambridgeshire were included. Glycaemic exposure was assessed in 2008-2009. The primary outcome was all-cause hospital admissions in 2010-2011. Adjusted relative risks for each HbA1c quintile were estimated using Cox models. Further relationships between HbA1c and risks were explored using spline models. Results: There was a non-linear relationship between HbA1c and the risk of all-cause, diabetes and vascular admissions (all P<0.001 for linearity test) with an HbA1c threshold of 61 (95% CI 55-66) mmol/mol [7.7 (95% CI 7.2-8.2)%]. For every 11 mmol/mol (1%) HbA1c above the threshold, the risks increased by 6.3% for all-cause admission, 6.4% for a diabetes admission and 15.9% for a cardiovascular admission (all P<0.001). The overall hospitalization risks of having an HbA1c above, rather than at, the threshold, were 19.1 16.3 and 54.3% greater, respectively. There were non-significantly greater risks of hospital admission below the threshold. Conclusion: In people with Type 2 diabetes, a non-linear relationship exists between HbA1c and the risk of hospitalization. A threshold of 61 mmol/mol (7.7%) was associated with the lowest rate of all-cause hospital admissions. Further research should investigate the causes of admissions below and above this threshold, with a view to developing strategies to reduce the excess hospitalization among patients with diabetes.