Transfusion medicine

• Calculate volume of fetal maternal hemorrhage (FMH) based on Kleihauer-Betke result:
  • [# pink / red (fetal) cells ÷ 2,000 cells counted) x maternal blood volume (5,000 mL is average)
• A 300 µg vial of RhIG will cover 30 mL of whole blood
• Therefore, volume of FMH ÷ 30 = vials of RhIG
• If the number of calculated vials is < 0.5, round down to the nearest whole number and add 1 vial
• If the number of calculated vials is ≥ 0.5, round up to nearest whole number and add 1 vial
• For example, if 8 fetal red cells are detected of 2000 cells counted
  • Volume of FMH = (8/2000 * 5000 mL) / 30 mL = 0.67 vials
  • Round up to 1 and add 1 vial
  • Answer: 2 vials should be administered

Contributed by Evelyn M. Potochny, D.O.

• History: 35 year old woman presenting to hospital after motor vehicle accident
• Blood type: O negative
• Laboratory testing:
  • Type and screen performed in the blood bank, followed by antibody identification which identifies reactivity consistent with anti-D plus anti-C
  • Adsorption studies were performed at an immunohematology reference laboratory, identifying anti-G and anti-C; anti-D not identified
• Clinical significance:
  • Anti-G is an antibody formed in almost all cases by Rh negative (D negative), G antigen negative patients. Anti-G reacts with epitopes on both the C antigen and the D antigen. Anti-G typically is seen in a D negative patient who has never knowingly been exposed to Rh positive blood, yet presents with an antibody that looks like a combination of both anti-D and anti-C.
  • This antibody can form through previous exposure via pregnancy or transfusion. A patient with anti-G would be transfused in exactly the same way as a patient who has the combination of anti-D and anti-C: with Rh negative (D antigen negative) and C antigen negative blood.
  • However, women of childbearing age with anti-G should receive Rh immune globulin during pregnancy to protect against the formation of a true alloimmunization against the D antigen, which could cause severe hemolytic disease of the newborn.
• Difficulty in finding compatible blood:
  • This patient can receive O, RhD negative, C antigen negative packed red blood cells, which accounts for approximately 2% of the blood inventory

A 31 year old G2P1 woman presents to a new medical center after having moved from out of state. She is 16 weeks pregnant and was referred to maternal fetal medicine for a positive antibody screen. Antibody identification reveals a pattern consistent with anti-D and anti-C. Additional blood samples are requested by the blood bank for adsorption testing at an immunohematology reference laboratory, as anti-G is suspected. In which scenario is RhIG indicated for this patient?

1. Anti-G, anti-C and anti-D are identified
2. Anti-D and anti-C are identified but anti-G is not identified
3. Anti-G and anti-C are identified but anti-D is not identified
4. Anti-G and anti-D are identified but anti-C is not identified

C. Anti-G and anti-C are identified but anti-D is not identified. Anti-G is an important consideration in the workup of a woman of childbearing age who appears to have anti-D and anti-C. Adsorption studies to discern the presence or absence of true anti-D should be undertaken to determine eligibility for RhIG in the interest of protecting against severe anti-D hemolytic disease of the newborn. Women of childbearing age who have not formed anti-D are eligible for RhIG. The presence or absence of of anti-G or anti-C does not influence RhIG administration.

Comment Here

Reference: Rh immune globulin

A 27 year old G1P0 receives 300 μg RhIG at approximately 28 weeks gestational age because her blood type is A, RhD negative. She later delivers a full term healthy boy at 39 weeks gestational age. Cord blood testing of the infant reveals he is O, RhD positive. Additionally, a fetal screen performed on a postpartum sample from the mother is positive, indicating fetal maternal hemorrhage, and a Kleihauer-Betke is reflexively performed in order to properly dose RhIG. How many total vials of 300 μg RhIG are required if 2,000 total cells are counted and 8 fetal cells are identified (and a maternal blood volume of 5,000 mL is presumed)?

1. 1 vial RhIG
2. 2 vials RhIG
3. 3 vials RhIG
4. 4 vials RhIG

B. 2 vials. Volume FMH identified by Kleihauer-Betke = (8 fetal cells / 2,000 total cells counted) x 5,000 mL maternal blood volume = 20 mL. 20 mL/30mL = 0.67 vial. In this case, 0.67 vial is rounded up to 1 vial and 1 additional vial is added, making the appropriate RhIG dose 2 vials.

Comment Here

Reference: Rh immune globulin