Precautions for venous blood collection are divided into precautions before blood collection, precautions during blood collection and precautions after blood collection. 1. Precautions before blood collection: Before blood collection, it is necessary to pay attention to the selection of suitable vascular sites, such as thick, light pain, not easy to cause hemolysis of the blood vessels, avoiding the selection of edema, hematoma, scars, catheters, fistulas, or vascular grafts, as well as mastectomy of the same side of the arm, or beyond any kind of venous infusion line sites. Ask the patient what is being examined and if they are fasting or taking anticoagulant medications. 2. Precautions to be taken during blood collection: Care should be taken during blood collection to ensure strict aseptic operation and sterilization according to regulations to avoid infection of the needle eye. 3. Precautions after blood collection: After blood collection, it is necessary to press for about 3~5 minutes, and avoid bathing within 8 hours, if local bruising occurs, use a warm towel to apply wet compresses after 24 hours, which can promote absorption. To summarize, there are a lot of things to pay attention to in order to make the operation of venous blood collection more accurate, and it is recommended that patients pay attention to rest, reduce the activities, and keep a calm mind.