Why do you apply a tourniquet during phlebotomy?

A tourniquet is applied during phlebotomy to temporarily restrict blood flow in the veins, making them more prominent and easier to locate and puncture. This enhances visibility and access to the veins, facilitating the collection of a blood sample. It also helps to minimize the risk of hemolysis and ensures a more accurate sample by preventing blood dilution from surrounding tissues. The tourniquet should be removed as soon as the needle is inserted to reduce discomfort and potential complications.