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Test ID: Direct Antiglobulin Test
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Direct Antiglobulin Test (DAT) / Direct Coombs Test (DCT)
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Direct Antiglobulin Test(DAT)- Tube Technique and Gel/Bead Technique
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Useful For
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- This test is performed to investigate possible hemolytic transfusion reactions, Hemolytic Disease of the Fetus and Newborn (HDFN), autoimmune hemolytic anemia, and drug-induced immune hemolysis.
- To determine if the red cells are coated in vivo with IgG or complement components
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Method name and description
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- Method Name and Description
- Is sometimes colloquially referred to as the Direct Coombs test, because it is based on a test developed by Coombs, Mourant, and Race.
- DAT is used to determine whether red blood cells (RBCs) have been coated in vivo with immunoglobulin, complement, or both.
- Different methodologies are used in Hamad Medical Corporation-Transfusion Medicine such as microplate/gel card/glass beads and tube techniques.
- Reflex Testing – (if applicable-one or more of the following tests)
- Blood Grouping
- Antibody Screening
- Antibody Identification
- Antibody Titration
- Prewarm Technique
- Acid Elution
- Antigen Phenotype
- Crossmatch
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Reporting name
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Direct Antiglobulin Test (DAT)
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Specimen type / Specimen volume / Specimen container
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- Neonates – 0 to 4 months – 1ml microtainer purple top (EDTA)
- Children – 4 months to 2 years – 2ml Purple Top (EDTA)
- Children – 2 years above and Adults - 4ml Purple Top (EDTA) or 6ml Pink top (EDTA)
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Collection instructions / Special Precautions / Timing of collection
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- Collection Instructions
- The intended patient being tested, and the blood specimen must be positively identified at the time of collection. The completed label must be attached to the tube of blood before leaving the bedside of the recipient.
- Special Precautions: Specimens are usually collected from veins in the antecubital area. Avoid collecting blood specimens from the following sites:
- Veins with running I.V fluids
- Areas with extensive scar tissue
- Areas with hematomas
- Edematous areas
- Specimen labeling requirements:
- The ID label must include the following information.
- Patient’s first, middle and last names (full name)
- Hospital health card number.
- Signature and identification number of the person collecting the specimen (information may be electronic or manual)
- The date and time of blood collection, (information may be electronic or manual)
- Location
- Specimen should be collected from one patient at a time
- Specimen is labeled and the request form signed before moving to another patient.
- Specimens should NEVER be relabeled
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Relevant clinical information to be provided
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Adequate clinical diagnosis of the patient shall be provided including
- History of previous transfusions if applicable
- Medication intake
- Diagnosis
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Storage and transport instructions
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- Specimens shall be transported at room temperature 20-24 degrees Celsius.
- Specimens should be transported immediately to blood bank and they will be processed as soon as it is received.
- Specimen retention
- 7 days from the time of collection
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Specimen Rejection Criteria
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Following are the reasons for Specimen rejection, but not limited to:
- Unlabeled, Mislabeled or relabeled specimen tubes.
- Specimen tubes that do not carry the date and signature/ initials of phlebotomist.
- Specimen collected in wrong blood containers.
- Specimen in leaking / contaminated containers.
- Quantity Not Sufficient.
- Specimen not accompanied by a test order.
- Specimen accompanied by improperly completed test order.
- Specimen accompanied by test order not carrying the signature and stamp of the requesting physician.
- Specimen and test order with mismatched patient’s identification details.
- Grossly Hemolyzed Specimens, except for patients, Severe Burns, Hemolytic anemias like Autoimmune hemolytic anemia and sometimes severe septicemia.
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Biological reference intervals and clinical decision values
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- DAT is positive when agglutination is observed.
- DAT is negative if no agglutination is observed
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Factors affecting test performance and result interpretation
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- Causes of False Positive Results:
- Spontaneous Aggregation, Improper saline storage, inappropriate blood sample, a small fibrin clot has formed in the tube neutralizing the AHG, and Septicemia.
- Causes of False Negative Results:
- Improper washing, improper technique, improper saline storage and PH and delayed testing, under centrifugation, a delay in adding AHG, AHG is inactive, Ineffective Anti-globulin serum and reagent sensitivity.
- A negative direct coombs does not necessarily mean that the red cells have no attached globulin molecules. Polyspecific and anti-IgG reagents detect as few as 200-500 molecules of IgG per cell, but patients may experience autoimmune hemolytic anemia when IgG coating is below this level.
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Turnaround time / Days and times test performed / Specimen retention time
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- Test is performed 24/7
- TAT – Routine 8 hours
- TAT – STAT 60 minutes
- All discrepant and abnormal results will be released in 3 working days
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