Blood draws have no effect on the body. When the body is sick, that is, when it is not feeling well, it will be examined in the hospital, and the doctor will usually issue a laboratory test to find out if there is any disease in the body. Blood tests include routine blood tests, biochemical tests, coagulation tests, hepatitis B tests, and so on. The amount of blood drawn is usually very small, only 2ml or at most 5ml per test tube, and if 10 test tubes are drawn, it may only be 10ml or 20ml of fluid. For a person’s entire blood, 20ml of blood is very little, sometimes when the body is good to donate blood, can donate 200ml, or even can donate 400ml, so the blood draw will not have an impact on the body.