Which tests can be conducted with a red plastic tube?

The red plastic tube is primarily utilized for tests that require serum. This includes tests such as serum pregnancy tests and blood alcohol tests, both of which analyze the liquid portion of the blood after it has been allowed to clot. The red tube does not contain any additives that could interfere with the assessment of these substances, making it suitable for tests that require serum rather than whole blood or plasma.

In contrast, tests like the complete blood count, PT (Prothrombin Time), and PTT (Partial Thromboplastin Time) require specific additives or anticoagulants that are present in other color-coded tubes, such as lavender or blue tubes. Therefore, the compatibility of the red plastic tube with serum tests solidifies it as appropriate for option C.