During a blood test, most people experience only mild discomfort. During a blood test, a small needle is inserted into a vein in your arm to collect a blood sample. You may experience: A quick stinging sensation when the needle is inserted into the vein. Mild pressure when blood is being collected. Slight soreness afterwards. A small bruise around the area where the needle was inserted. The discomfort may last only a few seconds, and tenderness usually disappears within a day or two. If you’re going to Pathology Glenroy for general blood work or special tests, you can expect some soreness around the injection site afterwards. Bruising is also normal. These symptoms should disappear in a day or two.