For phlebotomy, the blood is drawn from any part of the body, usually from the peripheral veins of the whole body, so it does not matter where the blood is drawn, but in the process of drawing blood, because the distribution of blood vessels of each patient is different, so the location of the blood will also be different. Most of the clinical sites for venous blood collection are in the middle of the elbow, which is generally thicker and connected to the deep veins in most patients, so the amount of blood collected at once can be guaranteed, but there are also many patients who have blood drawn from the back of the hand, which is actually peripheral venous blood, so blood from any location can be used for examination or detection of certain diseases. If the patient is suspected of having respiratory failure or acid-base balance disorder, arterial blood gas should be drawn for blood gas analysis, usually from the root of the thigh or from the side of the wrist, where the arterial pulsation can be touched.