Case 1: The Reverse Type That Won't Cooperate at 22:00
Mr. R is a 71-year-old man with IgM kappa Waldenström macroglobulinemia (IgM 4.8 g/dL, total protein 11.2 g/dL, serum viscosity 4.1 cP) admitted with melena and a hemoglobin of 6.8 g/dL. The pretransfusion sample reaches the blood bank at 22:00. Forward typing shows 4+ with anti-A and 0 with anti-B; anti-D is 4+. Reverse typing shows 2+ agglutination with both A1 and B cells at immediate spin, and the autocontrol is 2+ at immediate spin but negative at the AHG phase. The antibody screen is negative at AHG in gel. Immediate-spin crossmatches with two group A, D-positive RBC units are both 2+. When the plasma is removed, replaced with saline, and the tubes recentrifuged, both crossmatches become negative. He received two transfusions three years ago without incident.
1. What explains the reverse typing and immediate-spin crossmatch reactions, and what technique resolves the discrepancy?
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The pattern is nonspecific: 2+ reactivity with both A1 and B cells, plus a 2+ immediate-spin autocontrol, all of which disappear when plasma is replaced with saline.
- True isohemagglutinins would not react with both A1 and B cells in a group A person.
- A true antigen–antibody reaction does not disperse simply because the plasma is swapped for saline.
The cause is rouleaux: the high IgM paraprotein (and the elevated total protein) bridges red cells nonspecifically into stacks that read as agglutination, especially in plasma-suspended tubes at room temperature.
Resolve it with the saline replacement technique: after the immediate-spin reading, remove the supernatant plasma, add an equal volume of saline, resuspend, recentrifuge, and reread. Rouleaux disperses; true agglutination persists. Saline-suspended or washed cells are an acceptable alternative. Corroborate with a cold agglutinin screen, and note that the AHG phase is unaffected because rouleaux rarely survives washing.
2. What ABO/Rh should be reported, what should be transfused, and what would it mean if the reactions had persisted after saline replacement?
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Report group A, D-positive. The forward typing is unambiguous (4+ A, 0 B, 4+ D) and the reverse discrepancy is explained by rouleaux. Critically, ABO cannot be reported until the reverse discrepancy is explained - an unexplained discrepancy means group O RBCs and group AB plasma until it is resolved.
Group A, D-positive RBCs are correct. The AHG (IAT) crossmatch is the decisive phase here and is negative in gel; document that immediate-spin reactivity was rouleaux and that the units are serologically compatible at 37 °C/AHG.
If true agglutination persisted after saline replacement in both units and in the autocontrol, you would be dealing with a cold-reactive autoagglutinin (anti-I is common in Waldenström) rather than rouleaux. In that case: perform a cold agglutinin titer, prewarm the crossmatch, and - if there is no evidence of hemolysis, the titer is low, and the units are AHG-compatible - transfuse with a blood warmer and monitor. If incompatibility persists through AHG, escalate to the medical director before release rather than issuing silently.
3. Name two preanalytical hazards specific to this patient and one patient-safety consideration for the transfusion itself.
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Preanalytical hazards
- Cryoglobulin. Many Waldenström patients have one; a sample that cools in transit can precipitate, producing hemolysis, clotting, or spurious results (falsely low RBC counts, artifactual ABO problems). Prewarm the collection tube and transport it at 37 °C until the serum/plasma is separated.
- DAT positivity from the paraprotein. IgM and/or complement coating gives a positive direct antiglobulin test and can make the screen look positive; run a DAT and interpret it in context rather than assuming a new alloantibody.
Patient-safety consideration
The patient is hyperviscous (4.1 cP) at a hemoglobin of 6.8 g/dL. Transfuse slowly and in small aliquots, watch for volume overload, and coordinate timing with therapeutic plasma exchange - whole-blood viscosity rises after RBC transfusion, and a brisk 2-unit transfusion can precipitate hyperviscosity symptoms (headache, blurred vision, confusion) even while correcting anemia.