Identification of Unexpected Alloantibodies
Unexpected Alloantibodies
• Antibodies other than naturally occurring Anti-B or Anti-A
• Found in some 0.3 to 2 % of the population
• Immunization to foreign RBCs Antigens may result from:
o Pregnancy, Transfusion, injection with immunogenic material, immunizing event is unknown
o Once unexpected alloantibodies are detected in prenatal or pretransfusion testing, its specifically should be
determined and clinical significance assessed.
Clinically Significant Antibodies
• Cause HTR and/or HDFN
• Shortens anticipated survival of RBCs
• Active in vitro at 37 º C and/or by IAT
• Important in assessing the need to select blood for transfusion
• In prenatal testing, knowing the specificity and Ig class of an antibody helps predict the likelihood of HDFN
Laboratory Evaluation
• Serum or plasma can be used
• EDTA-anticoagulated blood sample is preferred to avoid uptake of complement components by RBCs that occur when clotted
blood samples are used.
• Medical History: Clinical diagnosis, Number of Pregnancies, Transfusion history and Drug therapy
• Test serum at all phases
• Testing of serum needs a panel of 8 or more group O reagent RBC samples of known blood group phenotype.
It is important to know how the serum under investigation reacts with the autologous RBCs to determine whether alloantibody, auto-
antibody or both are present in the serum.
Antibody Reactivity
• Reactivity of some antibodies may be increased by:
o Extending incubation time
o Lowering temperature
o Increasing the serum to cell ratio or using sensitive methods such as enzyme (FICIN) techniques
SINGLE ALLOANTIBODIES
• Usually easy to recognize serum displays
• Serum displays a reaction pattern (Additional antibodies may be present)
• Strength of observed reactions may be very according to:
o Dosage effect
o Variation in the amount of antigen of the cell
o Deterioration of the antigen during storage
o Presence of multiple antibodies
MULTIPLE ANTIBODIES
• Difficult to interpret results of serum using a panel of reagent RBCs
• Usually present when: observed pattern of reactive and nonreactive tests does not fit that of the single antibody; reactions of
variable strength are observed with the reactive samples that cannot be explained on the basis of the dosage; unexpected
reactions are obtained.
Rh ANTIBODIES
• If Anti-E is identified in the serum of transfusion candidate, the additional presence of Anti-C should be considered.
• Even when Anti-C is not detectable , it is advisable to select c-, E- (R1R1), blood for transfusion to R1R1, patients with Anti-E
since Anti-C is a common cause of delayed HTR.
• The reverse situation causes less of a problem. If Anti-E is identified the additional presence of Anti-E may not be determined
unless rare RzR1 are used. Also, almost all c- donor units will be E-.
ANTIBODIES TO HIGH INCIDENCE
• Suspected when all reagent RBC samples are reactive, but the auto control is non-reactive
• Patient’s siblings are often the best source of serologically compatible blood
Unexpected Alloantibodies
• Antibodies other than naturally occurring Anti-B or Anti-A
• Found in some 0.3 to 2 % of the population
• Immunization to foreign RBCs Antigens may result from:
o Pregnancy, Transfusion, injection with immunogenic material, immunizing event is unknown
o Once unexpected alloantibodies are detected in prenatal or pretransfusion testing, its specifically should be
determined and clinical significance assessed.
Clinically Significant Antibodies
• Cause HTR and/or HDFN
• Shortens anticipated survival of RBCs
• Active in vitro at 37 º C and/or by IAT
• Important in assessing the need to select blood for transfusion
• In prenatal testing, knowing the specificity and Ig class of an antibody helps predict the likelihood of HDFN
Laboratory Evaluation
• Serum or plasma can be used
• EDTA-anticoagulated blood sample is preferred to avoid uptake of complement components by RBCs that occur when clotted
blood samples are used.
• Medical History: Clinical diagnosis, Number of Pregnancies, Transfusion history and Drug therapy
• Test serum at all phases
• Testing of serum needs a panel of 8 or more group O reagent RBC samples of known blood group phenotype.
It is important to know how the serum under investigation reacts with the autologous RBCs to determine whether alloantibody, auto-
antibody or both are present in the serum.
Antibody Reactivity
• Reactivity of some antibodies may be increased by:
o Extending incubation time
o Lowering temperature
o Increasing the serum to cell ratio or using sensitive methods such as enzyme (FICIN) techniques
SINGLE ALLOANTIBODIES
• Usually easy to recognize serum displays
• Serum displays a reaction pattern (Additional antibodies may be present)
• Strength of observed reactions may be very according to:
o Dosage effect
o Variation in the amount of antigen of the cell
o Deterioration of the antigen during storage
o Presence of multiple antibodies
MULTIPLE ANTIBODIES
• Difficult to interpret results of serum using a panel of reagent RBCs
• Usually present when: observed pattern of reactive and nonreactive tests does not fit that of the single antibody; reactions of
variable strength are observed with the reactive samples that cannot be explained on the basis of the dosage; unexpected
reactions are obtained.
Rh ANTIBODIES
• If Anti-E is identified in the serum of transfusion candidate, the additional presence of Anti-C should be considered.
• Even when Anti-C is not detectable , it is advisable to select c-, E- (R1R1), blood for transfusion to R1R1, patients with Anti-E
since Anti-C is a common cause of delayed HTR.
• The reverse situation causes less of a problem. If Anti-E is identified the additional presence of Anti-E may not be determined
unless rare RzR1 are used. Also, almost all c- donor units will be E-.
ANTIBODIES TO HIGH INCIDENCE
• Suspected when all reagent RBC samples are reactive, but the auto control is non-reactive
• Patient’s siblings are often the best source of serologically compatible blood
