ABO Grouping Discrepancy in a Pre-Operative Patient
Mr. R., 61, is booked for a total hip arthroplasty in 18 hours with a 2-unit crossmatch request. His type-and-screen shows: forward grouping - anti-A 4+, anti-B 0, anti-D 4+, anti-C 0; reverse grouping - A1 cells 2+ at immediate spin, B cells 0; autocontrol negative. A group A typing from 6 years ago is on file. He has no transfusion history, no stem cell transplant, and no known cold agglutinin. Hemoglobin is 13.4 g/dL. Inventory: 4 group A units and 6 group O units. The technologist asks the supervisor whether the patient is group A with an unexpected antibody or group B, and whether the workup can wait until morning.
1. Which explanations fit this pattern, and what is your resolution plan for the current shift?
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The reactivity is confined to the reverse grouping, so the problem is an antibody against A1 cells, not a weak or missing B antigen. Group B is excluded because anti-B is absent both forward and reverse.
Differential:
- A2 (or A2B-type subgroup) with anti-A1 - most likely. Anti-A1 is a naturally occurring IgM that reacts with A1 cells but not A2 cells, and it does not react at 37 °C or AHG.
- Cold autoagglutinin (anti-I) - would usually give a positive autocontrol; here it is negative at immediate spin.
- Rouleaux - typically affects all reactions including the autocontrol.
- Subgroup with weakened A expression - excluded by 4+ anti-A forward.
- Chimerism/transplant or acquired B - excluded by history and by the absent anti-B.
Workup: test the patient's cells with Dolichos biflorus anti-A1 lectin (A1 cells agglutinate, A2 cells do not) and test the serum against A2 cells. Loss of reactivity with A2 cells plus a negative lectin reaction confirms A2 with anti-A1. If reactivity persists at 37 °C or AHG, extend to a cold panel and prewarmed technique. This is resolvable within a shift; do not delay surgery on the basis of the discrepancy alone.
2. If the workup confirms A2 with anti-A1, what blood would you issue, and how would you document and communicate the result?
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Anti-A1 is an IgM that is not active at 37 °C and is clinically insignificant; it has not been implicated in hemolytic transfusion reactions. The patient should be transfused as group A.
Products:
- Red cells: group A (A1 or A2 units are both acceptable), crossmatch-compatible. Group O is a safe alternative but is not required and should be conserved.
- Plasma-containing components: group A or AB.
- Platelets: group A or AB preferred; group O platelets acceptable if the titer is low.
Documentation and communication:
- Enter a comment in the LIS: patient is subgroup A2 with anti-A1, clinically insignificant; transfuse as group A.
- Flag the historical record so the discrepancy is not re-investigated on every admission.
- Notify the OR/anesthesia and the patient's physician in writing.
- Ensure the crossmatch is performed with the standard immediate spin/37 °C/AHG method; no special antigen-negative requirement applies.
3. The next morning the A1 cells react 4+ and the autocontrol is weakly positive at room temperature. How does that change your interpretation and plan?
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A positive autocontrol means the serum is reacting with the patient's own cells, so a cold autoantibody must be excluded before anti-A1 is accepted as the sole explanation.
Steps:
- Repeat the reverse grouping with a prewarmed technique (37 °C incubation, no room-temperature phase). A cold autoagglutinin will usually disappear; anti-A1 will persist against A1 cells but still not react with A2 cells.
- Test an autoabsorbed or cold-adsorbed serum if prewarming is inconclusive.
- Run a cold panel and, if indicated, a cold agglutinin titer to document the autoantibody.
- Recheck the Dolichos biflorus lectin result to confirm A2 status.
Interpretation:
- Prewarm abolishes reactivity and A2 cells are negative, with negative lectin - still A2 with anti-A1 plus an incidental cold autoantibody; transfuse group A with a prewarmed crossmatch if needed.
- Reactivity persists at 37 °C/AHG with A2 cells also reacting - treat as an autoantibody and investigate for cold agglutinin disease; transfusion must not be delayed in a bleeding patient, and group-compatible units are given with a documented serologic comment.