Aims/hypothesis: The prognostic importance of the ankle-brachial index (ABI) in individuals with diabetes is controversial. We aimed to evaluate the relationship between the ABI and the occurrence of micro- and macrovascular complications in individuals with type 2 diabetes.
Methods: The ABI was measured at baseline in 668 individuals with type 2 diabetes, and the individuals were followed-up for a median of 10 years. Multivariate Cox analysis was used to examine associations between the ABI and the occurrence of microvascular (retinopathy, microalbuminuria, renal function deterioration and peripheral neuropathy) and macrovascular (total cardiovascular events, major adverse cardiovascular events [MACE] and cardiovascular mortality) complications, and all-cause mortality. The improvement in risk stratification was assessed using the C statistic and the integrated discrimination improvement (IDI) index.
Results: During follow-up, 168 individuals had a cardiovascular event (140 MACE) and 191 individuals died (92 cardiovascular deaths); 156 individuals newly developed or experienced worsening diabetic retinopathy, 194 achieved the renal composite outcome (122 with newly developed microalbuminuria and 93 with deteriorating renal function) and 95 newly developed or experienced worsening peripheral neuropathy. The ABI, either analysed as a continuous or as a categorical variable, was significantly associated with all macrovascular and mortality outcomes, except for non-cardiovascular mortality. Individuals with a baseline ABI of ≤0.90 had a 2.1-fold increased risk of all-cause mortality (95% CI 1.3, 3.5; p = 0.004), a 2.7-fold excess risk of cardiovascular mortality (95% CI 1.4, 5.4; p = 0.004) and a 2.5-fold increased risk of MACE (95% CI 1.5, 4.4; p = 0.001). The ABI improved risk discrimination over classical risk factors, with relative IDIs ranging from 6.3% (for all-cause mortality) to 31% (for cardiovascular mortality). In addition, an ABI of ≤0.90 was associated with the development or worsening of peripheral neuropathy (2.1-fold increased risk [95% CI 1.1, 4.3]; p = 0.033), but not with retinopathy or renal outcomes.
Conclusions/interpretation: A low ABI is associated with excess risk of adverse cardiovascular outcomes, mortality and peripheral neuropathy development or worsening, and improves cardiovascular risk stratification. The ABI should therefore be routinely evaluated in individuals with type 2 diabetes.
Keywords: Ankle–brachial index; Cardiovascular outcomes; Microvascular complications; Mortality; Type 2 diabetes.