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Direct Antiglobulin Blood Test

Last updated July 15, 2019

Approved by: Krish Tangella MD, MBA, FCAP

The Direct Antiglobulin Blood Test (or DAT Blood Test) is a test to assess red blood cells’ sensitization to antibodies, such as immunoglobulin G (IgG) and other bodily defense proteins, such as complement.

What are the other Names for this Test? (Equivalent Terms)

  • DAT Blood Test
  • Direct Anti-Human Globulin Blood Test
  • Direct Coombs’ Antiglobulin Blood Test 

What is Direct Antiglobulin Blood Test? (Background Information)

  • Red blood cells (RBCs) are the principal ‘gas’ transport vehicles of the body. They display molecules on their surface (antigens) that the body recognizes, through its immune protein defenders (antibodies)
  • There are many antigens displayed by RBCs. The most abundant ones are antigens A, B, and D (also known as Rh)
  • An individual’s blood type is determined by the kind of antigens displayed by their red blood cells. RBCs of an individual with type A blood, display the A antigen; of type B blood, the B antigen; of type AB blood, both A and B antigens; and of type O blood, neither A nor B antigens
  • The body produces antibodies against opposing blood types. This is because a foreign antigen is considered invasive. Thus, an individual with type A blood, produces anti-B antibodies; with type B blood, anti-A antibodies, and so on
  • Unlike with A and B, the body does not produce anti-D antibodies as a preventative measure. Instead, anti-D antibodies are only produced, after contact with the D antigen has occurred
  • When an antibody, specific to an antigen, comes in contact with that antigen, the result is clumping (agglutination). In the case of RBCs, this result in their destruction - a condition termed as hemolysis
  • The Direct Antiglobulin Blood Test (or DAT Blood Test) is a test to assess red blood cells’ sensitization to antibodies, such as immunoglobulin G (IgG) and other bodily defense proteins, such as complement. The test is performed prior to blood transfusions and also to test for hemolytic disorders 

What are the Clinical Indications for performing the Direct Antiglobulin Blood Test?

Following are the clinical indications for performing a Direct Antiglobulin Blood Test:

  • Positive result from a RBC antibody screen
  • Rejection of donor’s blood by the recipient, during transfusion
  • To evaluate blood, prior to a transfusion
  • To evaluate mother’s blood during pregnancy
  • In an adult:
    • Fever, chills
    • Nausea
    • Low blood pressure
    • Skin and eye discoloration, especially yellowing
  • In a newborn:
    • Swollen tissues
    • Failure to thrive
    • Discoloration of the skin, especially yellowing 

How is the Specimen Collected for Direct Antiglobulin Blood Test?

Following is the specimen collection process for Direct Antiglobulin Blood Test:

Sample required: Blood

Process: Insertion of a needle into an arm vein.

Preparation required: No special preparation is needed prior to the test. 

What is the Significance of the Direct Antiglobulin Blood Test Result?

The significance of Direct Antiglobulin Blood Test is explained:

  • A positive test result may indicate:
    • Donor blood is incompatible with recipient blood
    • Hemolytic disease of the newborn (HDN)
    • Autoimmune hemolytic anemia
    • Viral infection
    • Lymphoma
    • Mycoplasma pneumonia
    • Systemic lupus erythematosus
    • Paroxysmal cold hemoglobinuria 

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario. 

Additional and Relevant Useful Information:

  • The Direct Antiglobulin Blood Test is often performed alongside a red blood cell antibody screen test
  • If this primary test results in agglutination, the RBC antibody identification blood test may be performed. It is a follow-up test that identifies the specific antibodies present in blood, to determine which ones are responsible for agglutination 

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

References and Information Sources used for the Article:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Aug. 3, 2014
Last updated: July 15, 2019