Interpreting results of testing with monoclonal Jk typing reagents in patients who have a positive direct antiglobulin test

A colleague in Northern California wonders how institutions interpret results of testing with monoclonal Jk typing reagents when a patient has a positive direct antiglobulin test (DAT; anti-IgG positive). According to one manufacturer's instructions, valid Jk typing conclusions cannot be made when a patient has a positive DAT and both monoclonal anti-Jka and anti-Jkb reagents are reactive with the patient's red cells. Some labs consider a negative patient result with K monoclonal antisera an appropriate control for Jk monoclonal reagents, since all 3 reagents (anti-K, anti-Jka and anti-Jkb) are monoclonal. The inquiring colleague wonders if it is appropriate to resolve Jk typing for a DAT positive patient using a negative K monoclonal reagent result.

In response to the above question, a group of highly experienced immunohematologists affiliated with a respected Reference Laboratory in Southern California do not think that a negative result with monoclonal anti-K is an appropriate control in this situation. This particular manufacturer’s instructions specifically say “a valid conclusion cannot be made.” Monoclonal antibodies can vary with respect to diluent ingredients and instructions for use. For example, one manufacturer’s monoclonal anti-Jka and anti-Jkb are diluted in isotonic saline containing bovine albumin (instructions are to incubate for 15 minutes at room temperature and then centrifuge for 60 seconds) but that same manufacturer’s monoclonal anti-K is diluted in a buffered protein solution containing bovine albumin and macromolecular potentiators (instructions are to incubate for 5 minutes at room temperature and then centrifuge for 20 seconds).

A good example of the unreliability of other monoclonals as controls was reported in 1995 (Rodberg K, Tsuneta R, Garratty G. Discrepant Rh phenotyping results when testing IgG-sensitized RBCs with monoclonal Rh reagents. Transfusion 1995;35Suppl:67S). Nineteen DAT positive patients typed as D+C+c+E+e+ (R1R2) using monoclonal reagents but were shown to be D+C+c–E–e+ (R1R1), D+C–c+E+e– (R2R2), D+C–c+E–e+ (R0r), or D–C–c+E–e+ (rr) following testing of chloroquine-treated RBCs. Some of reactivity was fragile and weaker than expected (1-3+); this can be a clue that the results may be suspect. The 6% albumin control suggested by the manufacturer was nonreactive and thus did not indicate the presence of the false positive results.

Their Reference Laboratory finds that treating DAT positive RBCs with EDTA glycine acid or chloroquine diphosphate, even if the resulting DAT on the treated RBCs is still positive, usually removes enough IgG from the RBCs so that valid typings with IgM reagents can be obtained.

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