Monospecific antihuman globulin (AHG) enables sensitized red cells to cross-link so that agglutination is visible. Enhancement media shorten the duration of incubation time and intensify the antibody/antigen interaction through multiple methods. Laboratories often stock several types to broaden their toolkit. It's crucial to consult the manufacturer's instructions to guarantee adherence to the correct protocols.
Low ionic strength saline (LISS) is the most common enhancement media. LISS reduces the ionic strength in the testing sample and causes a reduction of the zeta potential. It increases antibody uptake and decreases incubation time. Gel technology, which is widely used, operates in a LISS environment.
Polyethylene glycol (PEG) brings red blood cells (RBCs) closer together and concentrates antibodies by removing water molecules from the testing sample. It is the most sensitive of the enhancement media; strengthening almost all clinically significant antibodies. However, it will also enhance some clinically insignificant antibodies as well. PEG should not be centrifuged at the IS and 37°C phases. PEG can cause aggregates to form if the red cell/serum mixture with PEG added is centrifuged.
22% albumin reduces zeta potential, bringing the RBCs closer together and enhancing agglutination. Although not widely used for routine testing, it is still an effective enhancement medium, especially with antibodies in the Rh system.
Detection of some IgG antibodies can be enhanced with enzyme test methods. Blood group antigens are located on the surface layer of red blood cells. When a scientist is assessing the presence of a suspected antibody in a patient and tests against reagent red blood cells, they can manipulate these reagent cells with enzymes. This manipulation may artificially increase the expression of specific target antigens. Additionally, enzymes can be employed to remove target antigens, aiding in the evaluation of underlying patient antibodies or in further characterizing these antibodies.
Proteolytic enzymes (e.g., papain and ficin) denature some RBC antigens and remove negative charges from the RBC membranes. This reduces the zeta potential, bringing the cells closer together, and enhancing some blood group antibody/antigen reactions. Enzyme techniques are particularly useful in the identification of Rh antibodies and antibodies in the Kidd, Lewis, P, and I systems. However, enzymes reduce or destroy the reactivity of other antigens including Fy
a, Fy
b, M, and N. The effect of proteolytic enzymes on the S and s antigens are variable.
Technically, enzymes are categorized as “chemicals” rather than potentiating agents in most blood bank references. A number of other “chemicals” are available commercially for use in antibody identification and other blood banking procedures, including dithiothreitol (DTT), EDTA/glycine/acid (EGA), and chloroquine diphosphate. Regardless of which reagents are chosen for blood bank serologic testing, it is important for the blood bank scientist to be aware of the advantages and disadvantages of the reagent. Manufacturer’s directions must be followed and suitable controls included as appropriate.
