In the case of bruising on the arm after a blood draw, the bruising may occur because the patient did not press the site of the blood draw well after the draw, resulting in blood flowing from the blood vessels to the subcutaneous tissues, or the process of blood draw accidentally injured other blood vessels, resulting in subcutaneous bleeding and causing bruising on the arm, or it may be due to problems with the patient’s blood clotting function. If the bruise is not too large, the bruise will usually be absorbed slowly after a few days. If the area of the bruise is large, you can use cold towels for local cold compresses, and then local hot compresses after twenty-four hours, which can promote the local blood circulation of the patient and help the bruise dissipate quickly. If the patient’s bruise does not improve for a long time, it is recommended that the patient go to the hospital for a coagulation function test.