Quality Control

There are three controls necessary when typing for red cell antigens:

Control of the antisera

A positive control which ensures the reactivity of the antisera. The positive control cell should be weakly reactive for the antigen being tested, i.e., from a heterozygous donor.

hotlink A negative control which ensures the specificity of the antisera.

Red cells for these controls are selected from among the panel used for antibody identification.

Control of the cells being phenotyped

An autocontrol which ensures that the cells being tested will not spontaneously agglutinate with the antisera, even if they lack the corresponding antigen. This can happen, for example, if the red cells being typed have a positive DAT and are agglutinated by the protein in the antisera. Or, if the antigen typing is to be done by an IAT test, and the test cells have a positive DAT, they will agglutinate once antiglobulin serum is added, even if they lack the antigen being typed. Due to cost constraints some labs do not do autocontrols when typing donors and do not do an autocontrol on the patient if a DAT has been done earlier as part of the antibody identification.

In general, an autocontrol should parallel the conditions of the antigen typing test, except for being exposed to the specific antibody in the antiserum. Thus autocontrols will vary according to the type of antisera being used to antigen type. For example:

hotlink For saline-reactive antisera such as saline anti-D (which contains IgM anti-D in a low protein concentration of about 6 or10%, depending on the supplier), a suitable autocontrol (Rh control) would be

Negative reaction with any test that includes the patient's red cells in a low protein medium, e.g., ABO typing sera. Using this protocol, only patient's who appear to be group AB Rh(D) positive need to have a control set up.
Patient's red cells + 6% albumin (or whatever percent protein is in the typing sera.)

Note:An autocontrol when Rh typing using monoclonal/polyclonal blend anti-D (which contains a blend of IgM and IgG anti-D in a low protein concentration) would be similar to that for saline-reactive antisera as described above.

hotlink For "slide and modified tube" antisera (containing an IgG antibody in a high protein concentration of about 22% - 30%), a suitable autocontrol would be

patient's red cells + manufacturer's suppled control (i.e., the Rh control medium supplied with high protein anti-D)

For "IAT only" antisera (containing an IgG antibody which can only be detected by doing an IAT test and adding antiglobulin serum), the autocontrol would be

Direct antiglobulin test (DAT), i.e., wash patient's red cells 4 times and add antiglobulin serum. A negative DAT confirms that antigen-negative red cells will not agglutinate with antiglobulin serum.

QC of antigen typing