You have raised a number of good questions. From your experience I would think twice about donating blood in the future. The liklihood is your hematocrit was a bit low, and the loss of oxygen carrying capacity due to the donation affected your consciousness. That caused the headache and the weakness. Ballpark, one fifty-fourth of the blood is regenerated in the marrow every day. Usually these lumps disappear. Sterile one-time use equipment is used during the blood draw and there is virtually no chance of an infection. I guess it's possible. There could also be space aliens. Seriously. The chance of infection or introducing foreign matter into the blood stream during this procedure is extremely low. The blood banks have everything down pat. In any event, when they draw your blood a steel trochar (thin hollow needle) surrounded by a plastic tube is inserted into a vein, usually, but not always, the left or right median antecubital (in the crook of the elbow). The needle is withdrawn and the plastic tube remains in the vein while the blood is withdrawn. If the slanted tip of the needle punctures the wall of the blood vessel, there is leakage, which produces the bruise and swelling. Sometimes there is leakage at the point where the tube enters the wall of the vein. Use warm compresses, drink plenty of fluids and take it easy for a few days. In almost all cases these blood leak bruises disappear entirely within a few weeks. Sometimes this is due an an incompetent phlebotomist, but sometimes there is weakness within the vessel wall, and sometimes it is just bad luck. These complications happen, even with well-trained and conscientious personnel. Medicine is an art, as much as a science. I'm sorry about your bruise, but everything should turn out hunky-dory in a short time. If there are problems after six weeks, see a physician.
yes, happened to me too. Though not after giving blood, but after getting an IV put in and a drug injection for a minor surgery. The nurse had a difficult time getting the needle in (guess the vein was slippery). In any event, it hurt very badly going in and a month later there is still a bruise where she put the needle in a little further down my arm. My vein is hard, and there is a hard lump where my elbow crease is.... it's not hurting at all anymore. I'm just assuming she damaged the vein a little, Maybe there is some clotting going on.... but I assume it will go away.