The tempting mistake with a test name like carotid duplex is to guess what it means and move on. Reading the plain description first is the cautious habit, and it takes a minute for a reader in Tinley Park, Illinois.
What the test is
medlineplus.gov states: "Carotid duplex is an ultrasound test that shows how well blood is flowing through the carotid arteries." The same medlineplus.gov entry places those vessels for you: "The carotid arteries are located in the neck." Taken together, the test looks at blood flow in the arteries of the neck.
Reading you can do alone
The MedlinePlus Medical Encyclopedia has an entry on carotid duplex for readers who want the description in full. Reading it helps you understand the name on a referral. It does not tell you what your own test will show.
Where guessing should stop
Knowing what a test measures is different from knowing what your result says. A result belongs with a clinician who can explain it. Do not use the description of the test to decide for yourself that your neck arteries are fine.
The conservative choice
Ask rather than infer. If a clinician has ordered the test, ask what it is meant to answer for you and what happens after. MedlinePlus also has a page on carotid artery disease for readers who want general background.