Pencil & Paper method for calculating RhIg dosing...

NOTE: Often, the maternal blood volume is assumed to be 5L (5000 mL). More accurate TBV can be calculated using the weight/Hct (Calculator coming soon!) 

Step 1: Determine the Kleilhauer-Betke %.

Let's say you find 50 fetal cells out a total of 2000 total cells counted.

KB% = # of fetal cells/2000 total cells counted

= 50/2000

   KB = 2.5% 

Step 2: Convert KB% to Fetal whole blood volume

Fetal Blood Volume= KB% x 50 mL

= 2.5 x 50

FBV = 125 mL in this case

Step 3: Determine # of vials needed for coverage

# of vials = FBV/30 (avg RhIg coverage per vial)


=4.2 doses of RhIg to provide coverage

Step 4: Determine # of vials to administer:

To determine this, round the # of vials calculated in the previous step to the nearest whole number (round down if <5 in the tenths places. If 5 or above in tenths place, round up)


4.2 doses would round to 4

Then add 1 to this number. This provides a "safety dose" to make sure that all fetal blood cells are protected.

# of vials to administer= 4+1 = 5

Thus you would administer 5 vials

NOTE: This calculator automatically adds the 1 (safety vial) before rounding!

Thus, take whatever answer is  on the calculator & round to the nearest whole number to determine the amount of vials to administer to the mother

Consult with your attending!  This is not meant to provide medical advice. 

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These posts contain high yield information collected from various educational resources including textbooks, journal articles, educational websites and more. They are intended for educational use only and should NOT be taken as medical advice. I strongly believe the spreading of knowledge and depth of learned information should be encouraged in today's society rather than coveted. Membership is required to view these posts  and should be used solely for educational purposes only.