Symptoms begin within 6 hours of transfusion and include acute respiratory distress, severe hypoxemia, hypotension, fever and bilateral fluffy infiltrates on chest radiograph. Respiratory distress is due to noncardiongenic pulmonary edema. Patient may have shortness of breath. Signs and symptoms may be mild, and resolve after a few days, or they may be severe and result in pulmonary failure. Laboratory findings include leukopenia and hypocomplementemia.