Non-hemolytic transfusion reactions represent more than 95% of all transfusion reactions. Mild allergic reactions (e.g.urticaria) occur in 1 to 3% of recipients, and are one of the more common reactions to transfusion,accounting for 30-40% of transfusion reactions.Anaphylactic transfusion reactions, on the other hand , although dramatic and potentially fatal, are rare,with an estimated incidence of 1:20,000 to 1:47,000 transfusins.

The risk of sensitizing a recipient to a “minor” red cell antigen has been estimated at about 1% for each unit of blood transfused. Although the incidence of non-hemolytic febrile transfusion reactions has been reported to be as high as 5-7% , it depends on the definition of significant fever, the patient population and the blood products utilized, and probably occurs with 0.25-0.5% of units transfused. Congestive heart failure, induced by transfusion  of blood or its components, used to be frequent,but has been reduced by the use of components rather than whole blood and by improved clinical appreciation of the problem.Transfusion of bacterially contaminated blood is extremely infrequent.

Hemolytic transfusion reactions have been estimated to occur with a frequency of 1 in 6200 units transfused to 1 in 1400 units  transfused; the latter figure is likely more accurate. 10-25% of acute hemolytic transfusion reactions may prove fatal. Delayed hemolytic transfusion reactions have been estimated to occur with a frequency of 1 in 11,650 units transfused to 1 in 1500 units transfused; again , the latter figure is more likely to be closer to the true incidence.A recent prospective study in Hamilton. Ontario , suggested that delayed transfusion reactions occur in 1.5% of transfused patients, but had little clinical impact. Another recent report suggested that delayed serologic transfusion reactions(i.e.no clinical hemolysis ) occur in 0.66% of patients transfused, whereas delayed hemolytic transfusion reactions occcur in 0.12% of transfused patients.

Hepatitis B(HBV) post-transfusion hepatitis (PTH) has been reported to occur in a small number of recipients and account for 5-10% of all cases of PTH; the incidence and severity of transfusion – associated HBV infection is decreasing with HBsAg screening of donors.Although seldom transmitted by purified blood derivatives,HBV may be transmitted by single-donor components at a rate of 0.07% to 0.5% per unit transfused. Non-A , non-B (NANB) hepatitis now represents the major cause of PTH but the incidence has been markedly reduced with the introduction of the screening tests for the hepatitis C virus.The incidence now is reported as approximately 3%. Transfusion transmitted HIV occurs rarely with the donor screening procedures now in place and esmitates of risk range from 1:40,000 to 1:1,000,000 . Transmission of HTLV is rare, except for certain countries , e.g. Japan, the Caribbean. The incidence  of post transfusion CMV depends on the immunocompetence of the recipient; recent studies indicate an incidence of 1.2-1.5% in immunocompetent recipients with little or no morbidity.

Based on mandatory reporting to the FDA in the United States, most tranfusion-related deaths (excluding those due to hepatitis and to AIDS) are due to acute hemolytic transfusion reactions, with an estimated risk of 1:100,000 transfusions, although the incidence has fallen over the last decade from 81% to 57%  of transfusion-related deaths (1976-78 vs 1986-88). 68 fatal complications of blood transfusion were reported to the FDA between 1985-1988 , of which 29 (42%) were the result of ABO –incompatible transfusions. Amongst these were errors in collection of pre-transfusion specimen(7), clerical errors in the blood bank (8) , technical orrors in the blood bank (1) and errors on the nursing unit (11). Six fatalities were due to non-ABO antibodies . Non-hemolytic reactions were the cause of the fatalities in 26(38%) cases, due to bacterial contamination (9 platelets and 2 RBC) , acute respiratory failure (9) and anaphylaxis (6). Since under-reporting is likely, it remains difficult to obtain accurate estimates of the frequency and causes of transfusion related deaths.

It has been estimated that many (up to one third) adverse reactions ascribed to transfusion may be unrelated to the transfusion. However , it is important that any adverse reactions be reported to the hospital Blood

Bank for investigation and in turn, any serious complications be reported to the Blood Centre.

Conclusion:

Transfusion of blood and blood products is associated with certain risks that cannot be predicted or prevented. The physician should prescribe transfusion only when it is clinically essential and when no other from of treatment whould be as effective.