Taking blood. Nurse's hands inserting a needle into an arm vein to withdraw blood. The process of puncturing a vein is named venepuncture. The upper arm of the patient has a tourniquet (upper right) tied around it to make the veins stand out and be more visible. The blood is being withdrawn as a sample to test for white blood cells. The patient has chronic lymphoblastic leukaemia. The leukaemia disorders involve excessive production of white blood cells. Here, the excess white blood cells will be removed by passing the blood through a machine and back to the patient. The tests on the sample will gauge the success of the therapy.