compatibility testing

1. The Anti-Human Globulin (AHG) test, also known as the Coombs test, is an immunological
procedure used to detect antibodies or complement proteins that are bound to the surface of red
blood cells (RBCs). There are two types of AHG tests: direct AHG test and indirect AHG test.
Here's an overview of the principle, procedure, results, advantages, disadvantages, and
limitations of the AHG test:
Principle:
The AHG test is based on the principle that antibodies or complement proteins attached to RBCs
can be detected by using anti-human globulin reagents. These reagents contain antibodies that
recognize and bind to the antibodies or complement proteins on the RBC surface, causing
agglutination or other visible reactions.
Procedure:
Direct AHG Test:
Patient's RBCs are washed to remove any unbound antibodies or complement proteins.
AHG reagent containing anti-human globulin antibodies is added to the washed RBCs.
The mixture is incubated, and if antibodies or complement proteins are present on the RBCs,
agglutination or other visible reactions occur.
Indirect AHG Test:
Patient's serum (containing antibodies) is mixed with known RBCs (known as the screening
cells) that possess antigens on their surface.
The mixture is incubated, and if the patient's antibodies are present and have reacted with the
screening cells, they will bind to the antigens.
AHG reagent is added, and if the patient's antibodies are bound to the screening cells,
agglutination or other visible reactions occur.
Results:
Positive Result: Agglutination or visible reactions indicate the presence of antibodies or
complement proteins on the RBC surface. This suggests a positive AHG test, indicating the
presence of immune-mediated hemolytic anemia or other immune-related disorders.
Negative Result: Absence of agglutination or visible reactions suggests a negative AHG test,
indicating the absence of antibodies or complement proteins on the RBC surface.
Advantages:
Detects immune-mediated hemolytic anemia caused by antibodies or complement proteins.
Helps in diagnosing autoimmune diseases and transfusion reactions.
Essential for cross-matching blood before transfusions.

2. Disadvantages:
Requires skilled laboratory personnel to perform the test accurately.
False-negative results may occur if the antibodies or complement proteins are present at low
levels or are not detected by the specific AHG reagent used.
Limitations:
Does not identify the specific antibody or complement protein present; further testing is required
for precise identification.
Cannot distinguish between different causes of immune-mediated hemolytic anemia.
False-positive results may occur due to non-specific reactions or technical errors during the
testing process.