What is the purpose of using a tourniquet during venipuncture?

The use of a tourniquet during venipuncture is primarily to engorge the veins, making them more visible and easier to puncture. When a tourniquet is applied, it temporarily restricts blood flow in the veins of the arm, causing them to fill with blood and swell. This makes the veins stand out against the surrounding tissues, assisting the phlebotomist in locating a suitable vein for drawing blood. The improved visibility of the veins is particularly helpful in patients with small or difficult veins, as well as in pediatric cases where veins can be much harder to see.

The other options refer to different concepts or are not applicable in this context. For instance, while preventing blood from clotting is crucial in blood specimen handling, this is not the role of a tourniquet. Likewise, cooling the blood specimen relates more to storage and transport conditions than to the immediate venipuncture procedure. Supporting the patient's arm can be important for comfort and stability but is not the primary function of using a tourniquet.