Abstract

Background The ankle/brachial systolic blood pressure index (ABI), a noninvasive measure of peripheral arterial disease (PAD), is widely used in epidemiological studies. However, the normal ranges of the ABI in healthy populations and ABI criteria for the diagnosis of PAD in large population studies have not been critically evaluated. Methods and Results The San Luis Valley Diabetes Study (SLVDS) was designed to evaluate the prevalence and complications of non–insulin-dependent diabetes mellitus (NIDDM) in a biethnic population. The present study was conducted as part of the SLVDS to assess the prevalence of vascular disease in 1280 nondiabetic control subjects and 430 patients with NIDDM. The ABI criteria for PAD were developed in 403 healthy individuals with a low risk for cardiovascular disease. In these low-risk subjects, the average resting ABI value was 0.07 lower in women than in men. In both sexes, the dorsalis pedis ABI was 0.04 lower than in the posterior tibial artery, and the left leg ABI was 0.02 lower than the right leg ABI (all differences, P <.05). In the low-risk subjects, ABI values were lower after exercise than at rest and had similar differences by sex and leg as observed at rest. Using specific abnormal cutoff points for the ABI, we evaluated three criteria for PAD in the overall population: two abnormal vessels in the same leg at rest (both dorsalis pedis and posterior tibial arteries), one abnormal vessel per leg at rest, and an ABI abnormality only after exercise. Subjects classified with PAD by the two-vessel criterion had a higher frequency of claudication and the physical finding of an absent pulse compared with subjects without PAD or patients with PAD defined by the one-vessel or exercise criterion. Use of the two-vessel criterion identified an increased risk of PAD with increasing age, NIDDM, smoking, hypertension, and elevated cholesterol levels. In contrast, the one-vessel PAD criterion was associated only with increasing age and smoking, and exercise-diagnosed PAD was not associated with any cardiovascular risk factor except for male sex. Conclusions In low-risk subjects, the normal distribution and lower abnormal cutoff point values of the ABI differed by type of test, sex, ankle vessel, and leg. When these specific abnormal cutoff points were applied to the SLVDS population, the two-vessel abnormal criterion described patients with typical clinical characteristics of PAD and the expected associations of PAD with cardiovascular risk factors. These clinical characteristics and cardiovascular risk factor associations were less evident with PAD diagnosed by the one-vessel or exercise criterion. Therefore, an abnormal dorsalis pedis and posterior tibial ABI in the same leg at rest should be used for the diagnosis of PAD in epidemiological studies.