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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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