Final answer:
A phlebotomist should use a red-topped tube to collect a blood specimen for thyroid studies, as it allows the blood to clot and serum to be separated for analysis.
Step-by-step explanation:
A phlebotomist preparing to collect a blood specimen for thyroid studies should select a collection tube with a red top. This is because red-topped tubes are typically used for serum specimens, and thyroid function tests require serum. During the blood collection process, no anticoagulants are present in red-topped tubes, which allows the blood to clot. After the clot forms, the specimen is centrifuged to separate the serum from the clot for analysis.
It is important for a phlebotomist to choose the correct color-coded tube since different colored tops indicate different additives or lack thereof, which can affect the test results. For thyroid studies, ensuring that the blood clots and serum is obtained is essential for accurate testing.