Hemoglobin A1c, comorbid conditions and all-cause mortality in older patients with diabetes: A retrospective 9-year cohort study

Abstract

AimsTo examine whether hemoglobin A1c levels and comorbid conditions are related to all-cause mortality in a cohort of patients with type 1 or 2 diabetes receiving continuous care for 9 years. In patients with comorbid congestive heart failure (CHF), we test for ‘reverse epidemiology,’ or whether greater HbA1c values are associated with lower risk of mortality. MethodsThe population for this longitudinal cohort study was 8820 Group Health enrollees in the Seattle area with type 1 or 2 diabetes in 1997 and enrolled continuously from 1997 to 2006. Comorbid conditions were hypertension, coronary artery disease, congestive heart failure, depression, and chronic pulmonary disease. Mistimed HbA1c scores were addressed by multiple imputation, and Cox proportional hazards models estimated associations controlling for other risk factors. ResultsAbout 30% of the enrollees died in 1998–2006. CHF had the strongest association with all-cause mortality. Compared to enrollees with HbA1c≥7.1% (54mmol/mol) and <7.5% (58mmol/mol; 5th decile), enrollees with HbA1c<6.4% (46mmol/mol) had a significantly greater risk of death (HR range: 1.28–2.26). HbA1c>7.5% had HR<1.0 but were not significant. For enrollees with diabetes and CHF at baseline, HbA1c scores≥8.7% (72mmol/mol) had a significantly lower risk of death (HR range: 0.64–0.69). ConclusionsIn our patient population, HbA1c scores<6.4% have significantly higher all-cause mortality. CHF is a major determinant of all-cause mortality. Adults with comorbid CHF and high HbA1c scores have lower all-cause mortality.