A complete discussion oftransfusion reactions is beyond the scope of this manual. The incidence ofinfection through a blood transfusion has been greatly reduced, given theimprovements in donor screening and processing techniques. The mostsignificant infectious risk of transfusions is due to bacteriallycontaminated platelets. Platelets must be stored at room temperature and onan average 1 in 3000 bags are contaminated with bacteria proven by culture.The risk of an infection through a platelet transfusion is approximately 1in 20,000.

Mechanism

The risk oftransfusion-related acute lung injury (TRALI) is estimated at 1 case per5000 transfusions. It is characterized by acute onset of hypoxemia and theappearance of bilateral infiltration on chest X-ray within 6 hours oftransfusion of a plasma-containing product. The exact mechanism is unknown,but in a subset of patients donor antibodies (usually antiHLA) react withthe recipient’s white blood cells resulting in both release of intracellularinflammatory mediators and leukoagglutination in the lungs.