Questions and Answers
What can lead to a false positive result in a Direct Antiglobulin Test (DAT)?
Which situation requires the use of the Indirect Antiglobulin Test (IAT)?
Which factor does NOT affect the sensitivity of the Indirect Antiglobulin Test (IAT)?
How does an inappropriate serum to cell ratio affect the Indirect Antiglobulin Test results?
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In which situation would direct agglutination be observed in the IAT?
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What temperature is optimal for performing the Indirect Antiglobulin Test (IAT)?
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Which condition is NOT associated with the use of Direct Antiglobulin Test (DAT)?
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What is the primary purpose of the Direct Antiglobulin Test (DAT)?
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What could lead to a false-negative result in an antiglobulin test?
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Which preparation is expected to yield a negative direct antiglobulin test (DAT)?
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What reason might lead to a false-positive reaction in antigen-antibody interactions?
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Which of the following is an appropriate step to minimize false-negative results?
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What effect does a delay in adding antiglobulin reagent after washing have?
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How does inadequate washing of red cells affect the antiglobulin test?
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When preparing a control with O Rh(D) negative sensitized red cells, what must be ensured?
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What is the main consequence of having small fibrin clots in the cell suspension during testing?
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What indicates a positive antiglobulin test?
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What happens if too few washes are performed during the antiglobulin test process?
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Which of the following correctly describes the preparation of Coombs control check cells (CCC)?
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What does a negative antiglobulin test result suggest?
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How can positive control in Coombs control check cells be achieved?
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Which reagents would be found in a polyspecific antiglobulin reagent?
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What is a key reason for performing 3 to 4 washes in the antiglobulin test?
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What does the presence of agglutination after adding CCC indicate?
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Study Notes
False Positive Results
- Improper sample usage can lead to false positives, such as using clotted cells instead of EDTA.
- Spontaneous agglutination occurs when cells are heavily coated with IgM.
- Non-specific agglutination may happen with "sticky cells."
Types of Antiglobulin Test
- Two main types:
- Direct Antiglobulin Test (DAT)
- Indirect Antiglobulin Test (IAT)
Direct Antiglobulin Test (DAT)
- Detects in-vivo sensitization of red blood cells with immune antibodies (IgG) or complement components (C3b/C3d).
- Applications:
- Diagnosis of Hemolytic Disease of the Newborn (HDN).
- Diagnosis of Autoimmune Hemolytic Anemia (AIHA).
- Investigation of Hemolytic Transfusion Reactions (HTRs).
- Inquiry into drug-induced red cell sensitization (e.g., penicillins, phenacetins, quinidine).
Indirect Antiglobulin Test (IAT)
- Used to detect in-vitro sensitization of red cells when sensitization does not cause direct agglutination.
- Key uses:
- Checking weak D's in donor blood and Rh-negative pregnant women.
- Screening and identifying unexpected antibodies in serum.
- Compatibility testing.
- Detecting red cell antigens with specific antibodies (e.g., K, Fya, Fyb, Jkb).
Factors Affecting Sensitivity of IAT
- Temperature: Optimal incubation at 37°C; extremes can lead to false results.
- Serum-Cell Ratio: Increasing the ratio enhances antibody coating. Commonly used is 2:1 in saline suspension.
- Testing involves the use of anti-D serum diluted to a 1:4 titre; agglutination should repeat with diluted anti-D if necessary.
False Negative and Positive Results in Antiglobulin Tests
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False-negative reactions may occur due to:
- Inadequate cell washing leading to unbound antibodies.
- Delay in adding antiglobulin reagent after washing.
- Presence of small fibrin clots among cells.
- Ineffective or omitted antiglobulin reagent.
Inadequate Washing
- Insufficient washing can leave unbound antibodies neutralizing the antihuman globulin (AHG), preventing reaction with sensitized cells.
Delay in Adding AHG
- A delay post-washing may cause antibodies to elute, leaving free antibodies neutralizing the AHG and resulting in a negative test.
Presence of Small Fibrin Clots
- Fibrin clots may contain immunoglobulin and complement that neutralize the AHG, producing a false-negative result.
Antiglobulin Test and Interpretation
- Positive Test: Indicates antibodies are attached to the red cells, confirmed by visible agglutination after adding antihuman globulin.
- Negative Test: No antibodies attached, resulting in no agglutination after washing and adding antihuman globulin.
Coombs Control Check Cells (CCC)
- Used to verify test results:
- Positive control: Sensitized Rh(D) positive cells.
- Negative control: Unsensitized Rh(D) positive and sensitized Rh(D) negative cells.
- Agglutination of CCC verifies a negative result when original test cells remained unagglutinated.
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Description
This quiz explores the Direct Antiglobulin Test (DAT) and Indirect Antiglobulin Test (IAT), focusing on false positive results and specific methodologies. Delve into the impact of improper sampling and agglutination on test accuracy. Test your knowledge about these critical serological tests used in immunohematology.
