Local bruising after blood draw is mostly caused by the following: i. The short duration of pressure after blood draw causes the blood in the blood vessels to leak out into the subcutaneous, which leads to local bruising, swelling and pain. Second, the blood vessels from which blood is drawn are more brittle, thus causing blood to leak out into the blood vessels, resulting in bruising and other conditions. Third, the patient’s coagulation dysfunction or low platelet count, platelet dysfunction and other reasons, resulting in blood leaking out into the blood vessels, thus producing local bruising from the blood draw.