Blood compatibility testing: Difference between revisions

==Blood typing==

Upon direct testing by adding antibodies against A, B and/or Rh to patient blood, agglutination means that the patient has the antigen tested. Upon indirect testing by adding A or B antigen to patient plasma, agglutination means ''absence'' of the antigen in the patient (and thus the patient produces antibodies against it).

In the antibody screening procedure, an individual's plasma is added to a panel of two or three sets of red blood cells which have been chosen to express most clinically significant blood group antigens. Agglutination of the screening cells by the plasma, with or without the addition of anti-human globulin, indicates that an unexpected blood group antibody is present. If this occurs, further testing using more cells (usually 10–11) is necessary to identify the antibody. By examining the antigen profiles of the red blood cells the person's plasma reacts with, it is possible to determine the antibody's identity.

The image above shows the interpretation of an antibody panel used to detect antibodies towards the most relevant blood group antigens. Each row represents "reference" or "control" red blood cells of donors which have known antigen compositions and are ABO group O. A + means that the antigen is present on the reference red blood cells, and 0 means it is absent; nt means "not tested". The "result" column to the right displays reactivity when mixing reference red blood cells with plasma from the patient in 3 different phases: room temperature, 37°C and AHG (with anti-human globulin, by the indirect antiglobulin test).<ref name=UtahU>{{cite web|url=https://arup.utah.edu/media/AntibodyIdentification/Introduction%20to%20Antibody%20Identification.pdf|title=Introduction to Antibody Identification|author=Justin R. Rhees, M.S., MLS(ASCP)CM, SBBCM|website=University of Utah, Medical Laboratory Sciences|access-date=2020-12-18}}</ref>

* '''Step 1'''; Annotated in blue: starting to exclude antigens without reaction in all 3 phases; looking at the first reference cell row with no reaction (0 in column at right, in this case cell donor 2), and excluding (here marked by X) each present antigen where the other pair is either practically non-existent (such as for D) or 0 (presence is homozygous, in this case homozygous c).<br>When both pairs are + (heterozygous cases), they are both excluded (here marked by X), except for C/c, E/e, Duffy, Kidd and MNS antigens (where antibodies of the patient may still react towards blood cells with homozygous antigen expression, because homozygous expression results in a higher dosage of the antigen).<ref name="Mais 2014">{{cite book | last=Mais | first=Daniel | title=Quick compendium of clinical pathology | publisher=American Society for Clinical Pathology Press | publication-place=United States | year=2014 | isbn=978-0-89189-615-9 | oclc=895712380 }}</ref> Thus, in this case, E/e is not excluded in this row, while K/k is, as well as Js^b (regardless of what Js^a would have shown).<ref group=note>Besides from C/c, E/e, Duffy, Kidd and MNS, clinically significant dosage effects is rare but not impossible for other antigens, which thus may still be considered if subsequent cross-matching is reactive.</ref>