Question

A woman with blood type A Rh+ was admitted to a hospital for intestinal bleeding. She was transfused 4 units of blood 30 days prior to admission and also received another 4 units of blood 10 days prior to admission. When preparing four more units for transfusion, the alloantibody screen was positive along with a weak +DAT. The patients serum showed the antibody was anti-E. An elution was done and anti-Fya was identified.

1. What is the inconsistency between serum and eluate?

2. What tests should done?

3. What is the mechanism of this reaction?

Answer 1

1.What is the inconsistency between serum and eluate?

Elution is the process of extracting one material from another by washing with a solvent; as in washing of loaded ion-exchange resins to remove captured ions.

Serum is the fluid and solute component of blood which does not play a role in clotting. It may be defined as blood plasma without fibrinogens.

3. What is the mechanism of this reaction?

The direct antiglobulin test (DAT) commonly detects immunoglobulin G (IgG) molecules or complement fragments on the red blood cell (RBC) surface. If IgG antibodies are present then elution procedures can be performed to identify the specificity of these antibodies.

If the patient has not been transfused in the last three months, a positive DAT is expected to be due to an autoantibody because the only circulating cells are the patient’s own RBCs. However, it is possible that a transfusion—of which the patient is not aware—occurred at another facility. On the other hand, while most autoantibodies react with an antigen that is present on all RBCs, some autoantibodies have a relative specificity, such as to the e (little e) antigen.

Such antibodies are suspected when the patient’s serum is only reacting with reagent RBCs that express the specific antigen. In a patient who has been transfused in the past three months, a positive DAT may be due to an alloantibody attached to the RBCs from the transfused units, and the elution procedure is critical to make the antibody identification.