What does "fist clenching" do during blood collection?

Fist clenching during blood collection can indeed lead to inaccurate test results by increasing venous pressure. When a patient clenches their fist, it causes the muscles in the arm to contract, which can temporarily increase blood flow and pressure in the veins. This alteration in venous pressure can impact the composition of the blood being drawn, potentially leading to misleading laboratory results, particularly for tests requiring specific concentrations of substances like electrolytes or glucose.

This mechanism highlights the importance of proper technique during blood collection to ensure that results are accurate and reliable. Additional factors like hydration and patient positioning also play crucial roles, but the act of clenching can specifically interfere with the measurement process, making it a point of caution for healthcare professionals.