Coombs test, indirect (Blood antibody screening, Indirect antiglobulin test [IAT])
المؤلف:
Kathleen Deska Pagana, Timothy J. Pagana, Theresa Noel Pagana.
المصدر:
Mosbys diagnostic and laboratory test reference
الجزء والصفحة:
15th edition , p295
2025-11-15
29
Type of test Blood
Normal findings
Negative; no agglutination
Test explanation and related physiology
The indirect Coombs test detects circulating antibodies against RBCs. The major purpose of this test is to determine whether the patient has minor serum antibodies (other than the major ABO/Rh system) to RBCs that he or she is about to receive by blood transfusion. Therefore this test is the screening part of the type and screen routinely performed for blood compatibility testing (cross-matching in the blood bank).
Unlike the direct Coombs test that is performed on the patient’s RBCs, this test is performed on the patient’s serum. In this test, a small amount of the recipient’s serum is added to donor RBCs containing known antigens on their surfaces. This is the first stage. In the second stage of the test, Coombs serum is added. If antibodies exist in the patient’s serum, agglutination occurs. In blood transfusion screening, visible agglutination indicates that the recipient has antibodies to the donor’s RBCs. If the recipient has no antibodies against the donor’s RBCs, agglutination will not occur; transfusion should then proceed safely and without any transfusion reaction.
Interfering factors
* Drugs that may cause false-positive results include antiarrhythmics, antituberculins, cephalosporins, chlorpromazine, insulin, levodopa, methyldopa, penicillin, phenytoin, quinidine, sulfonamides, and tetracyclines.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: no
• Blood tube commonly used: red
Abnormal findings
- Incompatible cross-matched blood
- Maternal anti-Rh antibodies
- Hemolytic disease of the newborn
- Acquired immune hemolytic anemia
- Presence of specific cold agglutinin antibody
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