Final answer:
If no blood is flowing into the tube during venipuncture, the first step is to check the needle insertion and positioning. If the needle is correctly inserted, check for any obstructions in the venous access.
Step-by-step explanation:
If you have performed a venipuncture and no blood is flowing into the tube, the first step you should take is to check whether the needle is properly inserted into the vein. Ensure that the needle is at the correct angle and that it has penetrated the vein. You can also try repositioning the needle slightly if needed. If the needle is properly inserted and blood is still not flowing, then you should check if the venous access is obstructed. This could be due to a blood clot or a kink in the tubing. Gently tapping on the tube or repositioning it may help to clear the obstruction and allow blood to flow.