NHA Phlebotomy Certification Practice Exam

Application of the tourniquet on a patient's arm for longer than one minute may cause:

1. An increase in contaminated blood cultures

2. A clotted sample in the red top tubes collected

3. An increase in concentration of large molecules

4. Decreased pain and discomfort in the arm

The correct answer is: An increase in concentration of large molecules

Applying a tourniquet to a patient's arm for an extended period, particularly over one minute, can lead to increased concentration of large molecules in the blood sample drawn. This phenomenon occurs because the tourniquet restricts venous blood flow, causing blood to pool in the veins. As blood accumulates, there is a concentration effect, where cellular components, proteins, and other large molecules become more concentrated in the stagnant blood. This can affect laboratory results, particularly for tests that measure these constituents. While other options may sound plausible at first, they do not accurately reflect the physiological effects of prolonged tourniquet application. For instance, increased contaminated blood cultures typically results from improper handling or technique rather than the duration of the tourniquet's application. Similarly, while a tourniquet can cause stasis and impact clotting mechanisms, that would not specifically create a clotted sample in red top tubes; instead, it can lead to altered results without necessarily causing clotting. Lastly, prolonged application of a tourniquet would likely cause increased discomfort, not decreased pain, as it restricts blood flow and may cause swelling or sensation changes in the arm. Therefore, the correct focus is on the concentration of large molecules due to blood pooling.