Selection of compatible red cells for a patient with anti-M

A colleague in Ontario, Canada wonders how others would handle selection of compatible red cells for a 65 year-old male with liver and renal disease who is receiving dialysis and has recently developed anti-M, as described below:

• Transfused 2 units of RBCs on Sept. 12, 2004, at which time an antibody screen by GEL-antiglobulin method (GEL-IAT) was negative; a direct anti-globulin tube test (DAT) was negative
• Transfused 1 unit of RBCs on Sept. 18, at which time an antibody screen by GEL-IAT was negative
• Transfused 2 units of RBCs on Sept. 22, at which time an antibody screen by GEL-IAT was negative
• On Sept. 29 an order for 3 additional units RBCs is received, but the antibody screen by GEL-IAT is now positive showing anti-M specificity; DAT is positive (2+ by GEL, 1+ by tube due to IgG and complement). An acid eluate is negative. All RBC units given from Sept. 12th to Sept. 29th have been M positive.
• Nine more RBC units are crossed by GEL-IAT. Three of the crossmatched units are M-negative; all three are GEL-IAT non-reactive. However, of the other six crossmatched units, all of them are M positive, three are GEL-IAT reactive, and three are GEL-IAT non-reactive.

The inquiring Canadian does not feel comfortable using M+ RBC units in this case, even though three units are non-reactive in an indirect antiglobulin test. She wonders if others would use M positive units that are non-reactive in a GEL-IAT crossmatch, or insist on only using units that are BOTH GEL-IAT crossmatch compatible and M antigen negative?

The following responses have been received.

ADDENDA Oct .19, 2004

1. The supervising medical technologist at the transfusion service of the Editor's institution (LAC+USC Medical Center) reports that as a matter of policy they select for transfusion M-negative, GEL-IAT crossmatch compatible units for any patient in whom is discovered an anti-M reacting in the antiglobulin phase of testing. The presumption is that if the antibody it is reacting in the IAT phase of testing, it is likely to be an IgG antibody (or at least have an IgG component). The variability in the crossmatch results reported by the Ontario colleague is most likely due to a dosage effect of the M antigen expression, i.e. RBC units from MN heterozygotes showing no reactivity in a GEL-IAT crossmatch while RBC units from MM homozygotes show reactive GEL-IAT crossmatches. The LAC+USC colleague wonders if buffered GEL cards (without embedded anti-IgG) would be useful to differentiate between IgM anti-M and IgG anti-M, assuming appropriate controls were employed. For instance, if the anti-M was purely an IgG antibody, it should fail to react with homozygous M-positive red cells using the buffered GEL cards, while an IgM anti-M might show reactivity. Do others have experience with the use of buffered Gel cards to address this differentiation?

2. A colleague in Ohio reports that at his hospital, if a patient has an anti-M that is reactive ONLY at immediate spin, they will select donor RBCs that are antiglobulin crossmatch compatible, but they will not worry about the M-status of the donor unit. If the anti-M is reactive at 37 C or by an indirect antiglobulin test, they select donor RBCs that are both M negative and non-reactive by an antiglobulin crossmatch.

ADDENDA Oct. 29, 2004

3. An academic medical center in Michigan states that it has been their policy to issue crossmatch-compatible units for patients with anti-M, Le and P1. They do not routinely confirm the antigen-negative status of donor units when transfusing against those antibodies. However, they may switch from a LISS-tube to a saline/albumin crossmatch, since anti-M often gives enhanced reaction with acidic LISS reagents. Their policy is based on the recommendation of Cronin CA et al: Transfusion 1978;18:728-30.

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Ira A. Shulman, MD
CBBS e-Network Forum Editor & Moderator