Calculating RhIG Dosage

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The page below is a sample from the LabCE course Hemolytic Disease of the Fetus and Newborn. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Calculating RhIG Dosage

Using the estimated volume of fetal bleed determined by the KB test or flow cytometry, the number of vials of RhIG (300 µg) to inject is calculated as follows:
  • Number of vials of 300 µg RhIG = Volume of fetal bleed/30 mL
In the interests of safety, some American organizations recommend the following to deal with decimal points:
  • If the number to the right of the decimal point is <5, round down and add 1 vial (e.g., 1.4 = 1 + 1 = 2 vials).
  • If the number to the right of the decimal point is 5, round up and add 1 vial (e.g., 1.7 = 2 + 1 = 3 vials).
Sub-calculations:
  • Volume of fetal bleed: % fetal cells x maternal blood volume
  • Maternal blood volume: 70 mL/kg x weight (kg) (assume 5,000 mL if maternal information is unknown)