Human blood is basically in a non-coagulated state, in fact it is in a whole blood state. After the blood leaves the blood vessel, there will be a natural clotting process, and after the natural clotting, the supernatant will be precipitated, and the supernatant is serum. The supernatant is the serum. The plasma is the anticoagulant put into the test tube, the blood will not clot, and then the blood in the test tube is put into the centrifuge and the supernatant after centrifugation is the plasma. The serum or plasma used for different tests is different, the routine blood test is whole blood test, blood biochemistry, tumor marker test need to use serum, plasma for clotting factor test, need to use the upper plasma, so the nature of serum, plasma and whole blood are different, the requirements for the test is also different, according to the different requirements of the test to do the relevant processing.