The ankle-brachial index: a simple test for peripheral artery disease most people haven't heard of

The ankle-brachial index compares systolic blood pressure measured at the ankle to systolic blood pressure measured at the arm, and despite the test's underlying simplicity — it requires only a blood pressure cuff and a handheld Doppler device, nothing more technologically elaborate — the resulting ratio is a well-validated screening measure for peripheral artery disease, narrowing of the arteries supplying the legs, most commonly from the same atherosclerotic process that causes coronary artery disease.

The logic behind the ratio is straightforward: in a healthy circulatory system, blood pressure at the ankle should be roughly equal to or slightly higher than blood pressure at the arm, but significant narrowing in the leg arteries reduces blood flow and pressure reaching the ankle relative to the arm, producing a ratio below the normal threshold that flags likely peripheral artery disease requiring further evaluation.

Peripheral artery disease is genuinely under-diagnosed relative to its actual prevalence, in part because a meaningful share of affected patients don't experience the classic symptom (claudication — pain in the legs brought on reliably by walking and relieved by rest) clearly enough to prompt them to raise it with a physician, which is part of why ankle-brachial index screening in patients with relevant risk factors — smoking history, diabetes, known coronary artery disease — is recommended even without a clear symptom prompting the test.

The finding matters beyond the legs themselves: peripheral artery disease is a strong marker for atherosclerotic disease elsewhere in the body, including the coronary arteries, meaning a positive ankle-brachial index finding often prompts a broader cardiovascular risk evaluation beyond the legs specifically — the test functions as something of an accessible window into overall atherosclerotic burden, not just a leg-specific diagnosis in isolation.