Final answer:
The tourniquet should be released after the first blood collection tube is filled during a phlebotomy process. Capillary action assists with the blood draw, and during the hour following collection, serum will separate from the clotted cells in the glass tube for analysis.
Step-by-step explanation:
When a Certified Phlebotomy Technician (CPCT) is drawing five blood collection tubes, the tourniquet should be released after the first tube is filled but before the needle is taken out. This is usually done to ensure adequate blood flow and to minimize the potential for hemolysis or clotting within the tube, while also preventing venous stasis and reducing the risk of hematoma for the patient.
During blood collection, capillary action is the principle that allows the blood to be drawn into the narrow diameter of the glass collection tubes. The blood sample then sits in the glass tube for about an hour, during which time coagulation occurs if the tube does not contain an anticoagulant. The liquid component of the blood, known as serum, separates from the clotted cells. This serum is what the lab technician will harvest after an hour to continue with the blood analysis.