The prolonged non-elimination of arm bruises after blood sampling may be related to multiple puncture, improper pressure after puncture, and the presence of coagulation dysfunction. 1. Multiple puncture: Because some patients are fat, or it is difficult to locate the blood vessels during puncture, repeated puncture may be performed at the same site, resulting in tissue damage at the puncture site and prolonged bruising of the arm after blood sampling. 2. Improper pressure after puncture: After puncture and blood sampling, it is necessary to press the puncture site quickly when pulling out the puncture needle. If the pressure position is inaccurate or the pressure time is too short, it may cause bleeding from the vein at the puncture site to seep into the subcutaneous tissue. More bleeding will prolong the elimination of arm bruising. 3. With coagulation dysfunction: for patients with hematologic diseases, uremia, liver disease, etc.. There may be coagulation dysfunction, resulting in poor local coagulation, prolonged bleeding at the puncture site and prolonged elimination of arm bruising. When the arm bruise is not eliminated for a long time after bleeding occurs, it is recommended to consult a doctor in time, follow the doctor’s instructions for further examination, and carry out targeted treatment with the help of the doctor.