What is the purpose of using a tourniquet during a blood draw?

Using a tourniquet during a blood draw serves to engorge the veins, making them more prominent and easier to access. When the tourniquet is applied to the arm, it restricts blood flow from the venous side, causing blood to pool in the veins below the point of compression. This pooling leads to visible and palpable engorgement of the veins, which is crucial for successful venipuncture.

Creating this engorgement is particularly important in situations where the veins are small, deep, or difficult to locate. By enhancing the visibility and accessibility of the veins, the chances of successfully inserting the needle on the first attempt are significantly improved, thereby increasing patient comfort and reducing the need for multiple punctures.

While the tourniquet does play a role in temporarily affecting blood flow, its primary and most significant function is to promote venous engorgement, making it much easier to locate and puncture the veins effectively.