What type of test would require a red top tube?

The red top tube is primarily used for blood chemistry tests. This is due to its lack of additives, which allows for the serum to be separated from the blood cells after centrifugation. In these tests, the serum is what is analyzed for various chemical substances, enzymes, and other components within the blood.

Hematology tests, which typically measure components like red blood cells, white blood cells, and platelets, usually require tubes with additives such as EDTA for proper anticoagulation. Coagulation tests also need specific tubes, often containing sodium citrate, to ensure accurate results by preventing the blood from clotting. Blood gas analysis requires heparinized tubes to maintain the sample's integrity for the measurement of gases like oxygen and carbon dioxide.

Thus, while the red top tube is essential for blood chemistry, it is not suitable for the other types of tests, making it the correct choice for this question.