Do institutions that use the Gel method for ABO grouping encounter ABO grouping discrepancies due to failure of the test system to detect expected ABO antibodies?

A colleague in Nevada reports that according to a poster presentation at the 1997 AABB annual meeting entitled "ABO Grouping Experience with the Gel Test, authored by Kettler DS, Johnson MM and published in Transfusion 1997;37(Suppl)29S, it was suggested the Gel test is not as sensitive as standard tube test methodology for detecting ABO isohemagglutinins. According to Kettler's group, in 26 of 3,183 adult patients tested an ABO grouping discrepancy existed when using the Gel method because "expected" anti-A or anti-B were not detected. However, these ABO antibodies were easily (2+ to 4+) detected in 19 of the 26 patients by a standard tube test. Furthermore, in a study published by Langston MM et al in 1999 entitled "Evaluation of the gel system for ABO grouping and D typing" in Transfusion 1999;39:300-305, there was concurrence of the Kettler group's findings, that ABO isohemagglutinins were occasionally undetected when using a Gel method.

As a result of the Kettler data, the Nevada colleague's laboratory now routinely uses a tube test whenever an ABO grouping discrepancy is observed when ABO grouping is done by the Gel test. Since 1997, the Nevada laboratory has tested over 37,000 patients for ABO and in <1% of patients the 'expected 'anti-A or anti-B have not been detected by the Gel Test. About 75% of these ABO discrepancies are resolved by an immediate-spin tube test which 'shows' the expected ABO antibodies. In the remaining approx. 25% of patients, neither the tube method nor the Gel method 'shows' the 'expected' ABO isohemagglutins; for those patients they select cellular blood components based on the results of ABO FORWARD (cellular) typing using anti-A and anti-B gel typing reagents. (Editor's note: Some laboratories might select group O RBC units for patients who have an unresolved ABO grouping discrepancy.) In spite of the occasional ABO grouping discrepancy due to insensitivity of the Gel method to detect some ABO antibodies, in the experience of the Nevada laboratory, they have not seen a single instance where an ABO discrepancy workup with standard tube testing contradicted the initial ABO interpretation of a FORWARD typing test with anti-A and anti-B gel typing reagents. The Nevada colleague comments that the AABB Standards require ABO discrepancies to be resolved prior to issue of blood for transfusion. He wants to know if other colleagues believe that their data support discontinuing the practice of resolving an ABO grouping discrepancy, if the adult patient's plasma fails to react with known A1 and B cells in the gel test. In other words, if a FORWARD ABO grouping with a Gel method showed the patient to be group A or group B, but the plasma testing by a Gel method was non-reactive, would colleagues attempt to resolve such a discrepancy, or rely on the FORWARD grouping result? What ABO group would colleagues select for transfusion of blood products, in such a situation?

The following responses were received.

ADDENDA Jan. 31, 2003

1. An immunohematologist in Michigan reports that his group presented an abstract on this topic the same year as Kettler (see reference above), but from a slightly different angle. The Michigan colleague's group compared tube vs. gel to detect ABO incompatibility between eclectic A2B RBCs and group B plasma. [Steiner EA, Judd WJ. Detection of ABO incompatibility in gel. Transfusion 1997;37(S)29]. John Judd has graciously provided a MS Word file of their poster.
   
   Although the Michigan group did not see much difference in the sensitivity between gel and tube in their study, they would refer the Nevada colleague to the article by Steane and colleagues (referenced in the above cited poster) that includes a statement to the effect (and this is being paraphrasing) that there can be no substitute for...... a properly performed ABO typing test! To the Michigan immunohematologist, this requires resolving discrepancies whenever possible. He would certainly want to do so the first time such a discrepancy was encountered.
   
   So what entity (or entities) might give rise to an unreliable RBC (forward) typing result in gel tests when the serum is also nonreactive with A1 and/or B RBCs. The monoclonal anti-A and -B used in the gel cards is not known to react with B(A), acquired-B or polyagglutinable RBCs. An extremely remote possibility would be someone with a weak anti-A/B who also has made antibody to an ingredient (eg, blue or yellow dye) that is used to color the columns containing anti-A and anti-B. Such antibodies can interfere with the results of tube typing tests using unwashed RBCs, but the Michigan colleague has yet to hear that they have been implicated in a typing discrepancy using gel technique.
   
   If the Nevada correspondent feels comfortable omitting serum ABO tests on 1% of patients, why do a serum type at all? Which brings the Michigan colleague to report on the practice in Scandinavia where they do a full ABO type (RBCs and serum) twice, then do just the RBC type along with the antibody screen - in the same gel card - on all subsequently submitted samples. Such an approach (if the cards were made available here) would hopefully (in the opinion of the Michigan colleague) reduce costs of gel testing. In summary, the Michigan immunohematologist votes for problem solving the first time around, which is what they do now with discrepancies encountered by tube tests. And finally he adds, "Perhaps I'll change my opinion if and when we switch to gel".

ADDENDA Feb. 5, 2003

2. A physician and Head of Immunology at a blood bank in Spain reports the following about their use of gel tests for ABO/D typing. "The Gel test is becoming the standard for blood typing and crossmatch in Europe. At our donation centre we have been using the gel test (one card for ABO/D and another for antibody screening) for about two and a half years, with automated devices for pipetting and reading donor samples. Blood is collected in EDTA tubes. Technicians supervise the results and solve discrepancies. Previously, we used microplates for typing and gel cards for IAT. Up until now we have tested about 48,000 donations (4,000 of them new donors) and the discrepancy rate is as low as 1 in 1000. Hospital transfusion services in our region have performed about 100,000 patient ABO typings, RBC blood group confirmation, crossmatches and antibody screenings with gel cards and automated devices.

Although this is not "evidence-based medicine" I think it is a good amount of experience:

• The most frequent cause of discrepancy is failure to detect anti-B in A or O plasma samples. This can readily be corrected by the traditional tube test, which we usually perform at room temperature and sometimes at 4ºC.
• In some cases, discrepancies arise from an incorrect test cell preparation, so that the pipettor dispenses a lower amount of A or B cells into the well.
• Sometimes, irregular antibodies reacting at room temp., or even cold antibodies in the donor plasma, resemble an O serum, reacting with both A and B test cells.
• Different discrepancy rates can also be due to the different typing cards used, since (in his opinion) the performance of the Diamed gel is not exactly like that of the Ortho glass column or the Grifol gel."

In terms of the best practice to follow when an ABO grouping discordance is found using the gel method, the Spanish colleague recommends solving the discrepancy with the tube test. He concludes saying "they are not so frequent. I'd never do (except in an emergency) without a serum test. In any case you can always provide group O RBCs".

ADDENDA Feb. 6, 2003

3. In response to the comment #2 above, Sheryl A. Kochman, CBER/OBRR/DBA, Chief, Devices Review Branch (attribution used with permission) wants colleagues to be aware of a couple of points, especially users in the USA. None of the tests the physician in Spain refers to (Diamed gel, Ortho glass column; Grifol gel) are available in the USA. The DiaMed Gel Test is not available in the US and the MTS/Ortho Gel Test is not available outside of the Americas. They are manufactured in Europe and the US respectively and could be slightly different, but not so different as to change how discrepancies should be handled.

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