anti d injecton
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Here is a comprehensive overview of the Anti-D Injection (Rh Immune Globulin / RhIG):
Anti-D Injection (Rh₀(D) Immune Globulin)
What It Is
Anti-D injection is a preparation of human IgG antibodies directed against the D antigen of the Rhesus (Rh) blood group system. It is given to Rh(D)-negative individuals to prevent sensitization (alloimmunization) to Rh(D)-positive red blood cells.
Brand names: RhoGAM, HyperRHO S/D, WinRho-SDF, Rhophylac, MICRhoGAM
Why It Is Needed — The Problem It Prevents
When an Rh(D)-negative mother carries an Rh(D)-positive fetus, fetal red cells can enter maternal circulation (fetomaternal hemorrhage), especially during delivery or trauma. This triggers the mother's immune system to produce anti-D antibodies (initially IgM — which don't cross the placenta — then IgG on subsequent exposure).
In a subsequent Rh-positive pregnancy, the pre-formed maternal IgG anti-D antibodies cross the placenta and destroy fetal red cells, causing:
- Fetal anemia → cardiac decompensation → Hydrops fetalis
- Hemoglobin breakdown → Jaundice and Kernicterus
- Extramedullary hematopoiesis (erythroblastosis fetalis)
Rh disease is therefore uncommon in the first pregnancy but becomes progressively worse in subsequent ones. — Robbins, Cotran & Kumar Pathologic Basis of Disease
Mechanism of Action
Anti-D immunoglobulin works by passive immunization — the exogenous anti-D antibodies coat and rapidly clear any Rh(D)-positive fetal red cells from the maternal circulation before they can trigger the mother's own immune response. This prevents active sensitization.
Indications
1. Obstetric prophylaxis (primary use):
- Antenatal dose at 28 weeks gestation (routine)
- Postnatal dose within 72 hours of delivery of an Rh(D)-positive baby
- Following miscarriage/abortion, ectopic pregnancy, or termination (even early pregnancy — fetal cells can reach maternal circulation)
- Following invasive procedures: amniocentesis, chorionic villus sampling (CVS), cordocentesis
- Following abdominal trauma in pregnancy
- Antepartum hemorrhage (threatened/actual)
- External cephalic version
2. Transfusion:
- Prevention of isoimmunization in Rh(D)-negative individuals transfused with Rh(D)-positive blood or blood components
3. Immune Thrombocytopenic Purpura (ITP):
- In non-splenectomized, Rh(D)-positive patients (IV formulation only — WinRho-SDF, Rhophylac)
Doses
| Indication | Preparation | Dose |
|---|---|---|
| Antenatal prophylaxis (28 wks) | IM | 1500 IU (300 mcg) |
| Postnatal (within 72 hrs) | IM | 1500 IU (300 mcg) |
| Early pregnancy loss (<12 wks) | IM | 250 IU (50 mcg) mini-dose |
| Massive fetomaternal hemorrhage | IM/IV | Additional doses (guided by Kleihauer-Betke test) |
| ITP (Hgb ≥10 g/dL) | IV | 250 IU/kg |
| ITP (Hgb 8–10 g/dL) | IV | 125–200 IU/kg |
Conversion: 1 mcg = 5 IU — Harriet Lane Handbook
The standard full dose of 300 mcg (1500 IU) covers approximately 15 mL of fetal red cells (30 mL whole blood). If the Kleihauer-Betke test shows a larger fetomaternal bleed, additional doses are required.
Timing
- Must be given within 72 hours of the sensitizing event for maximum efficacy
- Can still offer partial protection if given up to 9–10 days after exposure
- Does NOT help if the mother is already sensitized (Coombs-positive / anti-D antibodies already present) — in that case, the pregnancy requires monitoring and management for existing disease
Contraindications & Cautions
- Contraindicated in IgA deficiency (risk of anaphylaxis)
- Do NOT give to Rh(D)-positive individuals (no benefit; wasteful)
- Do NOT give if mother is already sensitized to D antigen
- Use with caution in: atherosclerosis, hyperviscosity, coagulation disorders (thrombotic risk)
- May interfere with immune response to live vaccines (MMR, varicella) — timing should be considered
Side Effects
- Local injection site reactions (pain, redness)
- Mild systemic: fever, chills, headache
- Rare: hemolysis (especially with IV use in ITP — due to destruction of Rh(D)-positive red cells)
- Rare: intravascular hemolysis → anemia, renal insufficiency (IV use)
Key Points to Remember
| Given to | Rh(D)-negative mother only |
| Prevents | Maternal sensitization to D antigen |
| Does NOT treat | Already-sensitized (alloimmunized) mothers |
| Antenatal | 28 weeks |
| Postnatal | Within 72 hours of delivery |
| Early pregnancy events | Mini-dose (250 IU) if <12 weeks |
Sources: Harriet Lane Handbook (23rd ed.), Robbins & Cotran Pathologic Basis of Disease, Rosen's Emergency Medicine, Tietz Textbook of Laboratory Medicine
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