The blood test is done in a purple tube with an anticoagulant inside. When drawing blood, the tube is gently shaken from side to side to avoid blood clotting inside the tube. The blood test looks at the number of red blood cells, white blood cells and platelets in the blood vessels, not the serum. Therefore, when drawing blood, make sure that the blood does not agglomerate. Once it does, the blood test tube will be useless and a new blood draw will be required. Routine blood tests are very common in hospitals and can reveal the number of white blood cells, the number of red blood cells, the count of hemoglobin, and the number of platelets in the human body. Based on the various indicators, it can be inferred that certain diseases may have occurred in the body, such as inflammatory diseases when the white blood cells usually increase, and when anemia occurs the red blood cells and hemoglobin will decrease.