Investigation of suspected Hemolytic Transfusion  Reactions:

 When a hemolytic transfusion reaction is suspected:

If none of these tests indicate that incompatible red cells were transfused, it is almost certain that incompatibility can be excluded. Very rarely acute hemolytic transfusion reactions, that are presumably immune-mediated,occur in the absence of detectable antibody.

If the reaction is caused by red cell incompatibility , it is urgent for the laboratory to determine why the incompatibility was not detected before the transfusion. If the transfusion reaction was due to a mix-up of  patient samples or donor units,it is very likely that the error affects more than one patient. If the reaction was caused by an alloantibody , identification of the antibody is essential to obtain blood that is compatible.

Intravascular hemolysis may be due to other than immune mechanisms. For example , hemolysis may occur if the donor has an inherited intrinsic red cell defect, or if the cells have been subjected to physical or chemical stresses such as extreme temperatures or excessive infusion pressure or osmotic damage by hypotonic solutions.

Hypotension or shock may accompany transfusion without hemolysis and may be due to an anaphylactic reaction or the infusion of infected blood products.

b) Delayed Hemolytic Transfusion Reactions:

Despite previous sensitization to a red cell antigen , sometimes no antibody is detectable in the serum of a patient at the time of compatibility testing. Transfused blood that appears to be compatible then evokes a secondary or anamnestic immune response , i , e. , a rapid increase of antibody two to seven days following the transfusion. This antibody causes the destruction of the transfused red cells producing variable clinical manifestations, uaually less severe than an immediate hemolytic reaction. In their most benign from , delayed hemolytic transfusion reactions are asymptomatic, and may be detected only when the patient’s hemoglobin concentration falls. Other manifestations include fever, splenomegaly , jaundice , and (rarely) hemoglobinemia and hemoglobinuria . Transfusion recipients should be advised to notify their physician if any such symptoms occur after discharge from hospital.

The diagnosis of delayed hemolytic transfusion reaction is often made when more blood is cross matched several days after the initial transfusion. The direct antiglobulin test may be positive , and alloantibodies may be detected in the patient’s serum.

C) Febrile Reactions :

Fever during transfusion is the most common adverse reaction.

It may be due to :

       · destruction of transfused red blood cells
       · destruction of transfused white blood cells
       · bacterial contamination of the blood
       · reaction to proteins

A fever can have many causes unrelated to blood trtansfusion , therefore , a blood transfusion is not necessarily discontinued if a fever develops . Most febrile transfusion reactions are mild and may be treated (or prevented) by the administration of antipyretics while the transfusion is continued.

A severe febrile reaction requires the transfusion to be stopped and the laboratory to rule out the possibility of red cell destruction. In a multiparous or multi-transfused patient, a white

Cell antigen-antibody reaction is a more likely cause of fever than is a hemolytic transfusion reaction. The severity of the reaction and the clinical situation will affect the decision whether or not to continue the transfusion.

Most febrile transfusion reactions are due to alloantibodies reacting with donor white cells . Characteristically such reactions occur toward the end of the infusion of unit of red cells. Fever (an elevation in temperature of more than 2C ) in a patient who has never been transfused or pregnant should always be taken as an indication to stop the transfusion and look for red cell incompatibility, unless there is an obvious cause of fever unrelated to the transfusion.

Febrile reactions due to white cell antibodies can almost always be prevented by  processing the blood to reduce the number of white cells, e.g., Red Blood Cells, Leukocyte Depleted, Red Blood Cells, Washed or use of special filters (refer to Section II and V). Such processing should be considered in patients who have had severe repeated febrile reactions uncontrolled by medication and who require red cell transfusions.

d) Allergic Reactions:

(i)         (I)  Urticaria: Urticaria during blood transfusion is fairly common.                     Unlessextremely sever or accompanied by bronchospasm or other signs of
impending anaphylaxis, the development of urticaria is not an indication to stop the transfusion. The administration of an antihistamine to the patient generally relieves  the symptoms. The presence of urticaria alone should not cause the clinician to request the blood bank to do the time-cinsuming tests required to investigate a possible hemolytic transfusion reaction. For patients who have had urticarial reactions to blood transfusions , it is advisable to give an anthihistamine before the next transfusion is started. Allergic manifestations may be IgE-mediated reactions to an allergen in the transfused plasma. Most reactions are due to limited specificity alloantibodies to donor proteins, usually IgA.

(II)  Anaphylaxis: A life-threatening anaphylactic reaction occurs rarely during a transfusion of blood , plasma or other product as a result of potent class-specific IgA alloantibodies in the recipient’s plasma. These reactions cannot be predicted from the results of red cell compatibility tests. Individuals with inherited absence of IgA are at risk of severe anaphylaxis even during their first transfusion , but the first reaction may be relatively mild. Measurement of serum IgA and tests for antibodies to IgA should therefore be done in any patient who has had bronchospasm or hypotension resulting from a blood transfusion . If IgA is low or absent , or if anti-IgA is detected , such patients should be transfused with preparations free of IgA. If red cells are required, they can be prepared from the blood donations of random donors if well washed (usually six washings). A registry of IgA-deficient donors is maintained by the Blood Centre to provide plasma components deficient in IgA.