What is the main purpose of blood type screening before transfusions?

The main purpose of blood type screening before transfusions is to ensure compatibility between the donor's and the recipient's blood types. This compatibility is crucial because transfusing blood that is not compatible can lead to serious and potentially life-threatening reactions in the recipient. The immune system may recognize the transfused blood as foreign, leading to hemolysis (destruction of red blood cells) and various complications, such as fever, chills, and, in severe cases, shock or organ failure.

Compatibility is determined through blood typing, where the specific antigens on the surface of red blood cells of both the donor and the recipient are analyzed. Ensuring that the recipient's immune system can accept the donated blood is vital for a safe transfusion and is a standard practice in transfusion medicine.

The other options, while relevant to blood donation and transfusion in a broader context, do not address the critical and immediate need to ensure that the transfused blood is safe for the patient receiving it. Calculating blood pressure, determining the expiration date of blood products, and assessing a donor's nutritional status are important aspects of overall donor health and safety but are not the primary concern when screening for blood type compatibility before transfusions.