ABO & Rh Antigen System: Karl Landsteiner discovered erythrocyte surface carbohydrates (A, B agglutinogens) and IgM antibodies (anti-A, anti-B). The Rh(D) polypeptide determines positive ($+$) vs negative ($-$) status.
Transfusion Rules: $O^-$ red blood cells lack A, B, and Rh antigens, functioning as the Universal Red Cell Donor. $AB^+$ patients lack serum anti-A, anti-B, and anti-Rh antibodies, acting as Universal Recipients.
Blood Volume Dynamics: Total adult blood volume is approximately $70\text{ mL/kg}$ body mass ($55\%$ plasma, $45\%$ packed erythrocytes / hematocrit, $<1\%$ buffy coat leukocytes).
Operating Instructions: Select Donor and Recipient blood groups to test serum agglutination clumping and verify transfusion safety.