What type of sample is collected using a red top tube?

The correct choice is serum, as a red top tube is specifically designed to collect blood samples that will yield serum after the clotting process has taken place. When blood is drawn into a red top tube, it is allowed to clot without any anticoagulants. Once the blood has clotted, it is then centrifuged, which separates the liquid portion (serum) from the cellular components. This serum is then harvested for various laboratory analyses.

In contrast, whole blood would still contain all of the cellular components and hasn't been processed to separate the serum. Plasma is collected in tubes with anticoagulants, which prevent clotting, allowing the blood to remain liquid. Whole serum is not a typical designation for a sample type since serum itself is the liquid component that remains after clotting has occurred. Therefore, serum is the appropriate answer in the context of a red top tube usage.