同種免疫致敏

Buzzwords → Dx

Diagnostic Criteria

• DHTR: delayed Hb fall + positive DAT + alloantibody identified on screen.
• HDFN: maternal alloantibody + fetal/neonatal hemolysis (anemia, jaundice, hydrops).
• Platelet refractoriness: post-transfusion increment <2.5 × 10⁹/L per m² within 1 h, on ≥2 occasions.
• HLA antibody screen (panel reactive antibody, PRA): % reactivity to HLA panel.

Workup

• CBC + smear + retic + DAT.
• Antibody screen + identification (which RBC antigen?).
• Hemolysis labs (LDH, haptoglobin, indirect bili).
• Direct observation: schistocytes (microangiopathic), spherocytes (extravascular).
• Maternal anti-D titer (≥1:16 high-risk in pregnancy).
• Kleihauer-Betke or fetal cell flow for fetomaternal hemorrhage.
• MCA Doppler for fetal anemia surveillance.
• HLA antibody panel for platelet refractoriness investigation.

Treatment Algorithm

flowchart TD
  A[Suspected alloimmunization] --> B[Antibody screen + identification]
  B --> C{Type}
  C -- RBC alloantibody --> D[Identify antigen<br>antigen-negative units for future transfusions<br>life-long records]
  C -- anti-D in Rh-neg pregnant --> E[RhoGAM 28 wk + within 72 h delivery<br>+ extra dose if Kleihauer + or amnio / abruption]
  C -- DHTR active --> F[Supportive — monitor renal + hemolysis<br>future antigen-negative units]
  C -- HDFN risk in pregnancy --> G[MCA Doppler + intrauterine transfusion if severe<br>postnatal: phototherapy + exchange transfusion if needed]
  C -- platelet refractoriness immune --> H[HLA-matched or HPA-matched platelets<br>or rh ig if Rh+ donor / Rh- recipient]
  C -- platelet refractoriness non-immune --> I[Treat cause — DIC, sepsis, splenomegaly, drug-induced; ABO-matched]

Pearls / Pitfalls

• Anti-D HDFN prevention is RhoGAM at 28 wk gestation + within 72 h delivery (or after any sensitizing event: amnio, miscarriage, abruption, trauma, transfusion). Kleihauer-Betke quantifies fetomaternal hemorrhage to determine extra RhoGAM dose.
• Kidd antibodies (anti-Jk^a, anti-Jk^b) classic for delayed HTR — titer drops below detection between exposures, then anamnestic response. Cause severe intravascular hemolysis 7–14 days after transfusion.
• Antigen-matched RBCs in SCD (minimum Rh + Kell, ideally also Jk, Fy, S/s) reduce alloimmunization rate from ~30 % to <5 %.
• Platelet refractoriness algorithm:
  1. Confirm with corrected count increment (CCI) <2.5–7.5 at 1 h.
  2. Rule out non-immune causes: DIC, sepsis, splenomegaly, drug, fever, bleeding.
  3. If immune: test for HLA antibodies (PRA) → HLA-matched platelets; or anti-HPA → HPA-matched.
• HLA Class I antibodies (more common in alloimmunization) → use HLA-A and -B matched platelets.
• Anti-HPA (human platelet antigen) antibodies: cause neonatal alloimmune thrombocytopenia (NAIT) and post-transfusion purpura (PTP). NAIT prevention: matched maternal-paternal HPA antigens; treat with IVIG ± maternal corticosteroids antenatal.
• Daratumumab interferes with antibody screen — DTT-treated panel cells.
• Anti-Lewis antibodies are typically cold-reactive and clinically insignificant — don't need antigen-matched units.
• Lifetime medical alert for clinically significant alloantibodies — tell future transfusion sites; antibody titers may decline below detection but can re-emerge.
• Polyagglutination (T or Tn antigen exposure post-bacterial enzyme cleavage) — pneumococcal HUS in children → use washed RBCs (avoid plasma containing anti-T-antigen).
• Anti-CD38 (daratumumab): panagglutination on screen — DTT mitigation; document T&S BEFORE first dose.
• HLA-matched HCT reduces (but does not eliminate) GVHD; HLA antibodies in recipient pre-HCT can cause graft rejection (DSA — donor-specific antibodies).

Cross-references

• Transfusion Reactions
• Blood Groups + crossmatch
• SCD chronic transfusion
• Allo-HCT — DSA donor-specific antibodies
• Daratumumab T&S interference
• Lab Values — DAT, IAT, anti-D titer

相關題目

• Q-172 — DHTR — Kidd antibody anamnestic response
• Q-173 — Platelet refractoriness — HLA matching
• Q-174 — SCD — antigen-matched RBC transfusion

Sources