Alloantibodies Information and Courses from MediaLab, Inc.

Immune antibodies occur in the serum of individuals who become sensitized to foreign antigens through pregnancy or transfusion. IgM predominates in the primary response, IgG in the secondary response. Most react at 37°C and are considered clinically significant. Examples include antibodies in the Kell, Rh, Duffy, and Kidd systems. Immune antibodies can be classified as alloantibodies or autoantibodies.Alloantibodies Produced by exposure to foreign red cell antigens which are non-self antigens but are of the same species. They react only with allogenic cells. Exposure occurs through pregnancy or transfusion. Examples include anti-K and anti-E. Autoantibodies Produced in an autoimmune process and directed against one's own red cell antigens. React with patient's own cells and all cells tested. Can possibly mask the presence of other significant antibodies. It is very important to make sure that no underlying significant antibodies are present if an autoantibody is suspected. A positive direct antiglobulin test (DAT) or auto control could indicate the presence of an autoantibody. Examples include cold auto (P or I) or warm auto (Rh specificity).

Transplacental ITP may occur in newborn infants who are born to mothers with ITP. If the mother has had one baby born with thrombocytopenia, it is usually an indication that all subsequent infants will also be born with thrombocytopenia. A very small percentage of babies born with ITP will have severe thrombocytopenia. Neonatal alloimmune thrombocytopenia (NAIT) is caused by platelet destruction that is the result of alloantibodies stimulated by foreign antigens during pregnancy or blood transfusions. Platelet destruction by alloantibodies may occur in neonates if the mother lacks the platelet-specific antigen but the baby has inherited the antigen from its father. When maternal IgG antiplatelet antibodies cross the placenta, immune destruction of the neonate's platelets occurs. The major concern with both of these conditions is intracranial bleeding if the neonate's platelet count is less than 50 X 109/L. NAIT has a high mortality rate due to bleeding into the central nervous system. Prompt diagnosis of the condition and treatment is critical. The thrombocytopenia lasts on average 3 - 4 weeks postnatal until the maternal antibodies have cleared the newborn's system.

The first component of therapy is to stop the transfusion immediately. Vital signs must be closely monitored. Management involves treatment of hypotension and disseminated intravascular coagulation (DIC). It is essential to maintain blood volume and adequate renal blood flow. Diuretics, substances that increase urine output, may be administered. If the patient enters renal failure, dialysis must be initiated rapidly. It is impossible to prevent all hemolytic transfusion reactions. The purpose of pre-transfusion compatibility testing is to decrease the probability of a hemolytic transfusion reaction by performing ABO/Rh testing, detecting and identifying alloantibodies, and crossmatching compatible blood. Human error, the most common cause of hemolytic transfusion reactions, cannot be completely eliminated. Steps must be taken to reduce the possibility of human error in identification of patient samples, donor units, and recipients. Each person involved in the transfusion process, from collection of the blood sample to administration of the donor unit, must carefully adhere to each step outlined in the standard operating procedures. All appropriate protocols must be followed. Some examples are: Technologist checks blood sample to ensure proper labeling. Patient's previous transfusion records are examined and all transfusion testing is performed correctly and accurately. Technologist ensures correct unit is released from the blood bank. Transfusionist ensures the recipient is correctly identified.There must be a mechanism in place to train and assess all personnel involved in the transfusion process.