Antibody Identification

17 If the antibody screen is positive, the specificity of the antibody is identified by testing the serum against a panel of 8 to 20 Group O RBCs of varying phenotypes. The pattern of positive and negative reactions with these cells identifies the antigen against which the antibody is directed. Antibody identification is accomplished by the "crossing out" method which consists of identifying each cell that is negative and crossing out all of the antigens present on that cell. The panel should also be observed to:

Determine if the antibody is stronger at room temperature, 37oC , or antiglobulin phase
Determine if the autocontrol is negative or positive

From this information, one can determine:

Identity of the antibody
If the antibody is an alloantibody or alloantibody
If an autoantibody is cold or warm

Antibody Panel Interpretation

Thermal characteristic	Pattern of Reactivity	Autocontrol	Interpretation
Stronger at cold & weaker at warm temperature	One or few cells positive	Negative	Consider cold alloantibody such as MN, P, Le, etc.
Stronger at cold & weaker at warm temperature	All cells positive	Negative	Consider Vel, Tj^a, etc.
Stronger at cold & weaker at warm temperature	All cells posiitve	Positive	Cold autoantibody such as anti-I
Negative in cold & positive at warmer temperature	One or few cells positive	Negative	Consider clinically significant alloantibody such as Rh, Kell, Duffy, Kidd, Ss, etc
Negative in cold & positive at warmer temperature	All cells positive	Negative	Consider alloantibody to high frequency antigen KP^b, k, Lu^b, Js^b, Lan, Ge, At^a, U, etc
Negative in cold & positive at warmer temperature	All cells positive	Positive	Consider autoantibody with or without alloantibody

If a clinically significant antibody is identified, only red cells negative for the relevant antigen will be selected for crossmatching and transfusion. For example, if the antibody is anti-K, RBC of the appropriate ABO and Rh type will be tested with anti-K anti-serum and only K-negative red cells will be selected for transfusion. For added safety, an AHG crossmatch is also performed. For clinically insignificant antibodies, it is permissable to crossmatch units that have not been antigen typed.
When the antibody screen is positive, additional time is required to identify the antibody(ies), to find antigen-negative red cells, and to perform AHG crossmatches. This time can range from an hour to days if multiple antibodies, antibodies against high frequency antigens, or a mixture of autoantiobody and alloantibodies are present. If transfusion is medically necessary before compatible blood can be obtained, the attending physician and the transfusion medicine physician need to discuss the risk:benefit ratio of transfusing potentially incompatible blood.

An autoantibody is produced against a person's own red cells. When a patient has an autoantibody, the direct antiglobulin test and the autocontrol in an antibody panel will be positive. In addition, all cells in the panel will be reactive. If the antibody reactions are stronger at colder temperatures and weaker at warm temperatures, the patient probably has a cold autoantibody. If the antibody reactions are negative at colder temperatures and positive at warmer temperatures, the patient most likely has a warm autoantibody.

Last Updated on Monday, 18 July 2011