Blood Banking, quick reference 9 of 10
09 / 10 · Blood Banking
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), fragments of complement component 3 (C3), or both.1
DAT • sensitized in the body
Patient red cells
IgG, C3, or both already attached
AHG detects the existing coating
IAT • sensitized in the test
Patient serum or plasma + test cells
Antibodies bind during incubation
AHG detects coating formed in the test
In a tube method, AHG bridges sensitized cells, causing agglutination (clumping). Washing removes unbound globulin that could neutralize AHG.1
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| Comparison | DAT | IAT |
|---|---|---|
| Material tested | Patient red cells, commonly from anticoagulated blood. | Serum/plasma plus reagent cells, or donor cells for an antiglobulin crossmatch. |
| What is detected | Bound IgG, complement, or both, per reagent. | Antibodies reactive with test-cell antigens under the assay conditions, commonly IgG. |
| Common uses | Investigation of immune hemolysis, transfusion reactions, and hemolytic disease of the fetus and newborn.1 | Antibody screening and identification, prenatal testing, and antiglobulin compatibility testing.2 |
DAT interpretation
A positive DAT shows that the red cells are coated. Hemolysis is confirmed with other tests, such as bilirubin, lactate dehydrogenase, and haptoglobin. Weak coating can give a negative DAT.3
IAT interpretation
Test a positive screen with an antibody panel to identify the antibody. Weak antibodies or antibodies to antigens absent from the test cells may be missed.2
Read a gel card to grade six columns at the Blood bank.