What does a tourniquet do during the phlebotomy process?

A tourniquet plays a crucial role in the phlebotomy process by helping to visualize veins. When a tourniquet is applied above the site where blood will be drawn, it occludes venous blood flow while allowing arterial blood to continue flowing. This causes the veins to engorge with blood, making them more prominent and easier to locate. The increased visibility of the veins facilitates the phlebotomist's ability to select an appropriate vessel for venipuncture, ultimately enhancing the success rate of the procedure and reducing the chances of complications.

The other options describe effects that are not the primary purpose of a tourniquet. While reducing blood flow to the area is a physical effect of using a tourniquet, that effect is not the main goal; visualizing veins is the primary objective. The idea that a tourniquet increases pain perception does not hold, as its use is more about improving access to veins rather than affecting pain levels. Lastly, while a tourniquet may affect vasodilation indirectly, preventing it is not one of its intended functions during the phlebotomy process.