American Society for Clinical Pathology (ASCP) Histotechnician Certification Practice Exam

Applying a tourniquet above the venipuncture site is a reliable method to ensure effective blood flow during the procedure. The tourniquet creates temporary occlusion of the veins, leading to increased pressure in the veins below the tourniquet. This increased pressure distends the veins and makes them more prominent and easier to access. The engorged veins provide a better target for the needle, helping to facilitate the successful collection of blood samples while minimizing the need for multiple punctures.

Other methods, such as instructing the patient to clench their fist or warming the site, can also assist in improving venous visibility and flow, but they may not be as effective or consistent as the use of a tourniquet. Clenching the fist can constrict the veins and limit blood flow, while warming can help, particularly in cases where the veins are difficult to locate, but it does not provide the same immediate and significant effects on venous pressure as a tourniquet does. Using a smaller needle may not necessarily promote effective blood flow; larger gauge needles are often more effective for blood collection purposes.