Final answer:
A phlebotomist should ask the patient to release the fist during venipuncture after the tourniquet is removed and blood flows into the collection tube to prevent hemoconcentration.
Step-by-step explanation:
During a venipuncture procedure, a phlebotomist should ask the patient to 'release the fist' after the blood begins to flow into the collection tube and the tourniquet is removed. This is done to avoid the potential for hemoconcentration in the blood sample, which can occur if the fist remains clenched and the tourniquet is left on for too long. Maintaining the fist clenched exacerbates the tourniquet effect, potentially altering the test results by concentrating cells and other constituents in a smaller volume of plasma. During a routine venipuncture, the phlebotomist should request that the patient 'release the fist' after the blood has been collected. The phlebotomist will typically ask the patient to make a fist to help locate a suitable vein for blood collection. Once the blood has been drawn, the patient can release the fist to promote blood flow and prevent discomfort or injury.