Adsorption

In general, adsorption is the collection of a material on the surface of another material in a non-binding, non-permanent manner. In blood banking, adsorption refers primarily to the adherence of an antibody onto the surface of a red blood cell, described briefly below and in more detail in the linked definitions.

Before we get to that, you may have noticed that we blood bankers are REALLY picky about terms! If you want to really annoy a blood bank lab scientist (especially those who work in immunohematology reference labs), just try calling “aDsorption” (with a “d”) “aBsorption” instead! We get all kinds of irritated with that, probably unnecessarily, but the two really are different terms. ADsorption with a “d” means to bind something to a surface (think of a lint roller picking up stuff from your couch) while aBsorption with a “b” means to completely take something in and make it part of the absorbing substance (think of a sponge soaking up water). So, what we are doing here with antibodies sticking to RBCs is clearly “aDsorption,” since we are binding antibodies to the surface of RBCs rather than taking them inside of the RBC. I confess, I may have contributed to the confusion by describing adsorption in the past as “using red cells to soak antibodies out of plasma.” My apologies, you compulsive yet lovable blood bankers!.

Adsorption is used by blood bankers to bind antibodies to red blood cells in order to remove them from a particular patient’s plasma and better analyze the antibodies that might remain behind. This is commonly done in one of two ways:

• By using the patient’s own RBCs to remove autoantibodies (“autoadsorption“), or
• By using selected non-self RBCs to remove alloantibodies (“alloadsorption“).

Autoadsorption is used most often in the workup of warm autoantibodies, to remove autoantibodies so that underlying (“masked”) alloantibodies may be identified. Alloadsorption is necessary if the patient has been transfused recently (usually interpreted as within the past 3 months). Alloadsorption may also be used in complicated antibody identification workups, typically where there is more than one antibody present. In either setting, the idea is to get certain antibodies “out of the way” so that the antibody or antibodies “left behind” in the sample after the adsorption may be analyzed (the serum or plasma that is left behind is called “adsorbed serum“).

In addition, certain plasma antigens can passively bind (“adsorb”) to the surface of the red cell in a non-permanent way; the most famous of these are Lewis System antigens (for more, see my 2013 Lewis System video).

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