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LatticeMLSBlood banking · QUICK REFERENCE 09 / 09

DAT versus IAT

Where sensitization occurs and what the result can establish

The direct antiglobulin test (DAT) detects antibody or complement already coating the patient's red cells. The indirect antiglobulin test (IAT) tests whether antibodies in serum or plasma can coat test red cells during incubation.1

Sensitization is antibody or complement coating a red cell. Antihuman globulin (AHG) reacts with the coating specified on the reagent label, often immunoglobulin G (IgG) and/or fragments of complement component 3 (C3).1

DAT • sensitized in the body

Patient red cellsIgG and/or C3 already attached
AHG detects the existing coating

IAT • sensitized in the test

Patient serum or plasma + test cellsAntibodies bind during incubation
AHG detects coating formed in the test
Red cellRed cellIgGIgGAHG bridge

In a tube method, AHG bridges sensitized cells, causing agglutination (clumping). Washing removes unbound globulin that could neutralize AHG.1

The diagram illustrates the tube method. Gel and solid-phase methods separate and detect reactions differently; specimen and reagent instructions govern the method used.
ComparisonDATIAT
Material testedPatient red cells, commonly from anticoagulated blood.Serum/plasma plus reagent cells, or donor cells for an antiglobulin crossmatch.
What is detectedBound IgG and/or complement, per reagent.Antibodies reactive with test-cell antigens under the assay conditions; commonly IgG.
Common usesInvestigation of immune hemolysis, transfusion reactions, and hemolytic disease of the fetus and newborn.1Antibody screening and identification, prenatal testing, and antiglobulin compatibility testing.2