Final answer:
For platelet testing, the color of the tube top used is D) Light blue.
Step-by-step explanation:
For platelet testing, a light blue top tube is used because it contains sodium citrate, an anticoagulant necessary for accurate testing of platelets and coagulation factors. This light blue top tube contains sodium citrate, which is an anticoagulant that binds to calcium in the blood, preventing clotting. This is essential for accurate platelet function tests, such as a platelet count or coagulation studies like PT or aPTT, where it is crucial to assess the blood in a state that is as close to its natural, unclotted state as possible.