An older male patient is a long-term smoker and has shiny hairless legs. Which diagnostic test should you order?

In this scenario, the older male patient presents with shiny, hairless legs, a classic sign of peripheral arterial disease (PAD) often seen in long-term smokers. This condition is characterized by reduced blood flow to the extremities due to arterial narrowing or blockage. The shiny appearance and hair loss indicate poor perfusion, suggesting an underlying vascular issue.

The ankle-brachial index (ABI) is a straightforward, non-invasive test that compares the blood pressure in the patient's ankle with the blood pressure in the arm. A low ABI value suggests inadequate blood flow to the legs, which aligns with the patient's symptoms of shiny, hairless legs indicative of reduced circulation. This test is particularly useful in diagnosing PAD and assessing the severity of arterial disease.

Other options like arterial doppler, while potentially useful for evaluating blood flow and identifying blockages, are more complex and typically follow an initial assessment such as the ABI. Venous doppler focuses on the venous system and would not be appropriate in this case since the concern is arterial insufficiency. D-dimer is primarily used to rule out thromboembolic events and does not provide information about peripheral arterial circulation. Therefore, ordering the ankle-brachial index is the most appropriate first step in this clinical context.