Transfusion Calculations

Compatible Units Calculation

Used to determine the amount of units that statistically need to be searched in order to find antigen-compatible units.

$$\text{Units searched}=\frac{\text{Units required}}{(1\text{-}\mathrm{f}{\phantom{A}}_1)(1\text{-}\mathrm{f}{\phantom{A}}_2)(\dots )}$$

Where f₁ is the frequency of antigen 1, f₂ is the frequency of antigen 2, etc. For example, if 2x K- units are required and the frequency of K is 8%, then the equation is:

$$\text{Units searched}=\frac{2}{(1-0.08)}=\frac{2}{0.92}=2.17=3$$

The final number is rounded up to the nearest whole number.

Rh Immunoglobulin Calculation

Used to determine the amount of Rh Immunoglobulin to be provided to the mother based on fetal-maternal hemorrhage.

First, the estimated volume of fetal cells in circulation is calculated:

$$V_{\text{fetal blood}}=\frac{\text{Number of fetal cells per 2000 cells}}{2000}\ast 5000$$

The proportion of fetal cells per 2000 cells total is calculated and then multiplied by the approximate maternal blood volume.

Then, the RhIG dose is calculated (based on one 300 µg dose of RhIG, which protects against 30 mL of fetal blood) along with an additional 1 unit to provide a safety margin.

$$RhIG=\frac{V_{fetal}}{30}+1$$