Why the serum used in forward grouping?

In forward grouping, serum is used to determine the presence of specific antigens on the surface of red blood cells. By mixing a patient's red blood cells with known antibodies in the serum, clinicians can observe agglutination reactions that indicate the blood type. This process helps identify compatible blood for transfusions and ensures patient safety by preventing transfusion reactions. Ultimately, the serum acts as a key tool in blood typing and transfusion medicine.