How are positive direct antiglobulin test (DAT) results interpreted?

Updated: Jun 25, 2020
  • Author: Julie Katz Karp, MD; Chief Editor: Jun Teruya, MD, DSc, FCAP  more...
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Answer

Answer

The following indicate a positive direct antiglobulin test result: [4]

  • Agglutination observed after immediate centrifugation (usually seen when patient RBCs are coated with IgG)

  • Agglutination observed after centrifugation following room-temperature incubation (usually seen when patient RBCs are coated with complement)

There are many causes of a positive direct antiglobulin test, including the following: [3, 4]

  • Autoantibodies to intrinsic RBC antigens

  • Hemolytic transfusion reactions

  • Hemolytic disease of the fetus and newborn

  • Drug-induced antibodies

  • Passively acquired alloantibodies (eg, from donor plasma, derivatives, or immunoglobulin)

  • Nonspecifically adsorbed proteins (eg, hypergammaglobulinemia, high-dose intravenous immunoglobulin [IVIG], modification of RBC membranes by drugs)

  • Complement activation due to bacterial infection, autoantibodies, or alloantibodies

  • Antibodies produced by passenger lymphocytes (eg, in transplanted organs or hematopoietic components)

In the case of a positive direct antiglobulin test, three additional tests may be helpful. [4]

Monospecific AHG reagents can confirm which globulins are present.

The serum/plasma can be tested to detect and identify clinically significant antibodies to red cell antigens.

An eluate can be prepared from the sensitized red cells. An eluate displaces antibody from sensitized RBCs and recovers antibody in a usable form. The displaced antibody is then tested against a panel of reagent RBCs to determine the activity of the antibody. Eluate preparation frequently concentrates small amounts of antibody and may facilitate identification of weakly reactive antibody. When the eluate reacts with all the reagent RBCs tested, the patient most likely has an autoantibody. This is particularly true if the patient has not been recently transfused.


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