Liss Information and Courses from MediaLab, Inc.

Monospecific anti-human globulin (IgG) enables sensitized red cells to cross-link so that agglutination is visible.Enhancement media are sometimes used to further promote agglutination and reduce incubation time. Low ionic strength saline (LISS) is the most common enhancement media. LISS reduces the ionic strength in the testing sample and causes reduction of the zeta potential. It increases antibody uptake and decreases incubation time. 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. Centrifugation should be avoided when PEG is used. PEG can cause aggregates to form if the sample (red cell - serum mixture) with PEG added is centrifuged. Reaction readings should only be done at the AHG phase. 22% albumin: reduces zeta potential, bringing the RBCs closer together and enhancing agglutination. Albumin does not contribute much to antibody uptake. Longer incubation time is needed with this media than with the previously discussed media. Detection of some IgG antibodies can be enhanced with enzyme test methods. Proteolytic enzymes (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. Enzyme techniques are particularly useful in the identification of Rh antibodies and antibodies in the Kidd, Lewis, P and I systems. However, enzymes destroy some antigens including Fya, Fyb, M, and N. The effect of proteolytic enzymes on the S and s antigens are variable.

Before discussing crossmatch policies for women with passive anti-D likely due to RhIg, LIS-related issues will be outlined. A transfusion service's LIS and how it is configured determines under which circumstances an electronic crossmatch is possible.Regardless of crossmatch policy, almost all laboratories use a special designation or code in their LIS for anti-D likely due to RhIg. Often this designation is entered in the patient history comment field and not the antibody field, thus eliminating the need to remove the passive anti-D from the antibody field when the antibody disappears. Using this policy, once the passive antibody no longer reacts, the patient becomes eligible for an electronic crossmatch without the need to remove the antibody history.In essence, using a special designation for passive anti-D allows the lab to bypass the LIS's normal requirements for patients with clinically significant antibodies, i.e., allows them to omit doing an IAT crossmatch. Examples of how RhIg-derived anti-D is designated in lab information systems: Passive anti-D (eg., code 'PD', 'DPAS', etc.); Probably passive anti-D; Anti-D consistent with RhIg; Anti-D due to RhIg.Depending on the LIS, other variations are possible.

In this case the patient's antibody has disappeared from the plasma by adsorbing to transfused donor red cells. It is detectable but unidentifiable in the post-transfusion red cell eluate. Several trial and error procedures exist to enhance weak antibodies. Which methods will enhance the reactivity of a given antibody depend on its characteristics. Methods to investigate weak antibodies include: Use a higher plasma to red cell ratio (add more antibody-containing plasma or eluate) Increase incubation time (if consistent with manufacturer instructions, if applicable) Use enzyme-treated panel red cells (enzymes enhance IgG antibodies in Rh and Kidd blood systems but denature some antigens, e.g., Fya, Fyb, S) Try alternative antibody detection methods, e.g., if using LISS routinely, try polyethylene glycol (PEG) or column agglutination methods such as gel, providing they have been validated for use in the TS laboratory.