Rh Immune Globulin (RhIG)

Rh Immune Globulin (RhIG)

Overview

  • Rh Immune Globulin (RhIG) contains anti-D antibodies.
  • It is administered to Rh-negative mothers who are not already allo-immunized to anti-D and who have potential exposure to Rh-positive red blood cells (RBCs).
  • Administration is via intramuscular injection using a pre-measured 1 ml syringe with an attached needle.

Dosing

  • There are two main doses: micro dose and full dose.

Micro Dose RhIG

  • Indications:
    • After abortion, miscarriage, or termination of ectopic pregnancy.
    • Administration should occur at 12 weeks gestation (antepartum).
  • Dosage:
    • Micro dose = 50 \mu g of anti-D.
    • Protects against 2.5 ml of Rh+ RBCs or 5 ml of Rh+ whole blood (WB).

Full Dose RhIG

  • Indications:
    • After amniocentesis/cordocentesis.
    • Following abdominal trauma during pregnancy.
    • Antepartum hemorrhage.
    • Postpartum.
  • Administration:
    • Following an abortion or miscarriage after 12 weeks gestation.
    • At ≥ 28 weeks gestation (antepartum).
    • Within 72 hours postpartum:
      • When the infant is Rh-positive or the fetal Rh is unknown (e.g., fetal demise/stillborn, miscarriage, etc.).
      • When the mother has not developed an allo-anti-D.
  • Dosage:
    • Full dose = 300 \mu g of anti-D.
    • Protects against 15 ml of Rh+ RBCs or 30 ml of Rh+ WB.

Antepartum Injection of RhIG

  • If a mother receives an antepartum RhIG injection, a weak AHG reaction may be detected in the antibody screen (ABS).
  • The antibody identification panel will reveal a weak reacting anti-D.
  • After verifying the patient's chart for evidence of antepartum RhIG administration, this anti-D Ab is reported as "passive anti-D," not "allo" anti-D.

Calculation for RhIG Dosage

  • Formula: Fetal cells volume (from Kleihauer-Betke (KB) test result) / 30 = # of syringes to be given.
  • When calculating the number of RhIG vials, include one decimal place (X.X).
  • Rounding:
    • If the decimal is < 0.5, round down (e.g., 2.2 = 2).
    • If the decimal is ≥ 0.5, round up (e.g., 2.7 = 3).
  • Always add 1 to the calculated dose to ensure an adequate dose (e.g., calculated dose is 2 + 1 = 3; calculated dose is 3 + 1 = 4).

Rh Factor Sensitization Prevention

  • Rh-negative mothers who have not been previously sensitized to the Rh factor receive an intramuscular injection of Rhesus Immune Globulin to prevent antibody formation.
  • The injection is administered at 28 weeks of pregnancy and within 72 hours of the birth of a confirmed Rh-positive baby.
  • Sensitivity to blood titers is checked 6 months after the last Rhogam injection following the birth of an Rh-positive baby to rule out false positives.
  • If titers remain positive after 6 months, sensitization has occurred.

Other Treatments: IV RhIG

  • Following accidental transfusion with Rh+ RBCs into an Rh-negative recipient.
    • Intramuscular injection is not the appropriate therapy when the blood volume is larger than 30 ml. Use IV Rh Immune Globulin, e.g., WinRho@.
    • The blood bank (BB) can calculate the amount to be given based on the quantity of Rh+ RBCs transfused.
    • Consult the BB Medical Director.

Immune Thrombocytopenia Purpura (ITP)

  • Treatment of ITP:
    • The BB does not issue IV Rh Immune Globulin for ITP treatment; this may be a pharmacy intervention.
    • ITP is a blood disorder caused by a low platelet count, resulting in petechiae.
    • RhIG elevates the platelet count in these patients.
  • Anti-D Immune Globulin can be used as a substitute for IVIg for maintenance therapy, especially in patients with contraindications to splenectomy.
  • Coats red cells with IgG and allows red cells to serve as a decoy for splenic macrophages.
  • Patient must be Rh-positive.
  • Not effective after splenectomy.
  • Designed to cause hemolytic anemia; hemoglobin may drop as much as 3g/dl.
  • Intermittent dosing may allow patients to avoid splenectomy.