Methods to obtain appropriate reaction strength when performing daily reagent QC using gel cards  

A colleague in Los Angeles is curious to learn how others obtain a reaction strength of between 1+ to 3+ when performing daily QC on antibody detection red cells when using anti-IgG MTS GEL cards. The College of American Pathologists (CAP) Laboratory Accreditation Checklist item TRM.31400 (Phase II) requires that a laboratory documents 1+ to 3+ reactivity when performing QC on antibody detection red cells, regardless if the method for antibody detection testing employs a tube method or a non-tube method.

The following responses have been received.

ADDENDA Feb. 10, 2004

1. A colleague from Ohio reports that in order to obtain a 1+ to 3+ reactivity of a positive control when QCing their anti-IgG MTS GEL antibody detection test cards, they dilute with saline the 'Ortho QC antibody' that is provided in the Ortho QC kit. Interestingly, the saline dilution required to achieve the 1+ to 3+ reactivity of the positive control ranges from 1:5 to 1:40. This range of dilutions required to achieve 1+ to 3+ antibody reactivity in the GEL-AHG QC testing is seen in the six transfusion services within the colleague's integrated health care system. She reports that the stability of the 'Ortho QC antibody' is affected by the dilution, and they have found it necessary to prepare additional diluted 'Ortho QC antibody' antibody during the in-date period of the reagents being QCed. This is done in order to maintain the desired reactivity, as the antibody reactivity eventually drops below 1+ reaction strength.
   
   
2. The Editor reports that at the USC Kenneth Norris Cancer Hospital laboratory (where he is transfusion service medical director), that they use a set of R1R1, R2R2 and rr reagent red cells with anti-IgG MTS GEL cards for routine antibody detection testing. The daily Quality Control (QC) of the antibody detection red cells is accomplished using Immucor's corQC antiserum, which consists of a weakly reactive blend of human anti-A, anti-B, anti-D, and anti-c. The laboratory dilutes the corQC antiserum by mixing 100 microliters of the antiserum with 2.5 mL of 6% albumin. The diluted antiserum gives a 1+ to 3+ GEL-AHG result when tested against each of the R1R1, R2R2 and rr reagent red cells.
   
   
3. A colleague in Colorado reports that in her laboratory, they consistently obtain a 3+ reaction during QC testing of all three reagent antibody screening red cells when using the anti-IgG MTS GEL card with the Immucor corQC antibody undiluted.
   
   Editor's Note: At my hospital, we routinely observe a 4+ reaction, if QC is done with undiluted Immucor corQC antibody. This is the reason that we dilute the corQC antibody so that it reacts between 1+ and 3+ during QC testing (see response #2 above).

ADDENDA Feb. 19, 2004

4. A colleague from a 4-hospital system in Southern California can echo the findings of the colleague from the Pacific Northwest on both counts. They have found that dilutions of the Ortho Confidence Antibody are stable. They prepare their dilutions in 8% Bovine Albumin and have validated these dilutions for a 7-week period, extending one week beyond the antibody reagent expiration date so that they can retain the same expiration as the original reagent. She mentions that they encountered some concern from an FDA investigator, since the Ortho Confidence System direction insert clearly states "These reagents are ready to use as furnished. Do not dilute them." After reviewing their validation and making several phone calls to his FDA superiors and to Ortho, the investigator finally concluded that what they were doing was "OK". They also experienced some frustration in trying to find one dilution that will work for all 3 cells in the 3-cell screen. She states, "I can understand that there is no perfect commercial reagent that will meet the CAP specifications for all of the antibody enhancement media in use by transfusion services. However, with the increasing popularity of the MTS Gel I think that the manufacturer should provide an appropriate QC reagent for this method that would not require dilution." She would also like to know from sites that are using Ortho's ProVue what they are doing for QC of antibody detection cells, since she has this instrument under consideration.
   
   Her institution also prepares daily 0.8% dilutions of the antibody screening cells, yet use the manufacturer's prediluted 0.8% antibody identification panel as the first step in identification. They also have seen a number of examples of antibodies detected with the "in-house" dilutions of antibody screening cells, but are non-reactive with the manufacturer's prediluted panel. The most frequent examples are antibodies in the Rh system. However they have encountered this with Fy and Jk antibodies as well. She states that they also take the extra step of preparing fresh dilutions from one of their backup 3% antibody identification panels or employing PEG as an alternate method to enhance and identify these antibodies when they are unable to do so with the prediluted panel.

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