What is AHG test?

The AHG crossmatch is done by incubating the recipient serum/plasma with the donor’s red cells and adding anti-human globulin reagent to detect any antibody coating of the donor red cells. It is really just an indirect antiglobulin test (IAT).

What is the purpose of AHG test?

The antiglobulin (AHG) test was invented by Coombs, Race and Mourant in 1945 and is sometimes called the Coombs test after its main inventor. It is the single most important test we have for detection of red cell antibodies.

What is an AHG reagent how is it prepared?

Anti-Human Globulin (AHG) is prepared from serum of rabbits immunized with purified human IgG to provide the Anti-IgG. Non-specific activity in the rabbit serum is absorbed and removed. The anti-IgG is then blended with anti-C3d (BRIC 8) which is an IgM antibody derived from spleen cells of an immunized mouse.

What is the principle of Antiglobulin test?

PRINCIPLE: The direct antiglobulin test (DAT) is used to demonstrate the presence or absence of IgG and C3 on the surface of red blood cells. Red blood cells that possess IgG and/or C3 absorbed to their surfaces are referred to as sensitized red blood cells.

What are the two types of AHG reagent?

There are two types of AHG reagents, polyspecific and monospecific reagents.

How do you test for weak D?

The way to detect weak D cells reliably is to do a test for weak D (usually called a Du test). The Du test is an indirect antiglobulin test using the patient’s red cells and an IgG anti-D. An IgG anti-D must be used because antiglobulin serum contains anti-IgG.

Why are AHG reagents color green?

The Anti-IgG component is derived from rabbits while the Anti-C3d is a monoclonal IgM antibody. Both reagents are colored green to enhance process control. The reagents may also be used to demonstrate the in vitro coating of human red blood cells with antibody molecules and/or complement (polyspecific AHG only).

What techniques are necessary for weak D testing?

Due to the reduced number of Rh D antigens on the RBC surface, the RBCs will not agglutinate when using anti-D typing reagents with an immediate-spin technique. Detection of weak D requires an enhancement technique to detect it, typically by using an indirect antiglobulin (IAT) procedure.

What does a positive IAT signify?

A positive test result could mean your blood and the donor’s blood are not compatible. A positive test result during pregnancy could mean your baby has hemolytic disease.

Why is AHG green?

Green AHG is made by adding erioglaucine and naphthol yellow S to the blend. The test procedure is based on the agglutination principle, where human immunoglobulins and/or complement attached to the red cell surface agglutinates in the presence of the polyspecific AHG indicating a positive result.

What is weak D blood type?

The weak D phenotype is a weakened form of D antigen that in routine D antigen testing will react with some anti-D but not with others (when 37 C incubation or an immediate spin is given). Weak D RBC has D antigen but fewer in number as compared to normal Rh D-positive red cells.

When is testing for weak D optional?

Test for weak D, if initial Rh typing appears to be D-negative (Optional -not mandated by blood safety standards). If weak-D testing is performed, antihuman globulin reagents that do not contain anti-complement activity would be recommended in order to avoid agglutination due to complement coating of maternal cells.

Which is the last phase of the AHG test?

AHG Phase. The last of the three so-called “phases” or “stages” of testing serum and red cells for compatibility, most commonly in test tubes (the first two are the immediate spin and 37oC phases).

Where does the word AHG come from in a blood test?

During this step, we add anti-human globulin (yes, that’s where “AHG” comes from) to the serum-RBC mix, centrifuge the tube, and examine to see if the AHG agglutinates red cells that were coated with antibody (usually IgG) in earlier steps. This process is really just an indirect antiglobulin (Coombs) test.

When to add AHG to a test tube?

When known sensitized cells (check cells) are added to the same tube at the end of the test, free AHG will react with the sensitized cells and facilitate the agglutination. Label a test tube according to the lab number and patient’s name.

How does the indirect antiglobulin test work for AHG?

Indirect Antiglobulin Test (IAT, IDC, IAGT) After reading the saline 37°C part of the test, the red cells are washed well 3 – 4 times to remove all unbound protein. The washing stage is crucial, because if any unbound protein (IgG) remains, it could neutralize the AHG serum and cause a false negative.