What type of specimen does a red stoppered tube yield?

A red stoppered tube is primarily used for the collection of blood samples that will yield serum. This type of tube does not contain any additives that would prevent the blood from clotting. As a result, when blood is collected in a red stoppered tube, it is allowed to clot. After clotting, the tube is typically centrifuged to separate the liquid portion from the cellular components. The liquid that remains after this process is serum.

Serum is the clear fluid that remains once the clot has formed and the cells have settled at the bottom. It contains various substances such as electrolytes, hormones, and antibodies but lacks clotting factors, which are used up during the clotting process.

In contrast, whole blood includes all components of blood—both the cellular elements and the liquid plasma—without separation. Plasma, obtained from tubes containing anticoagulants, retains the clotting factors, thus allowing for the evaluation of coagulation tests. Clotted blood refers to the state of the blood once it solidifies after collection, which describes the process rather than the resulting specimen type. Hence, the correct answer indicates the specific liquid component derived from a red stoppered tube, which is serum.