RhoGAM Dose Calculator

RhoGAM Dose Calculator Explanation and Clinical Context This calculator estimates the volume of fetal whole blood and the number of 300 microgram vials of Rh immune globulin required after a positive Kleihauer Betke test or after counting fetal and total red blood cells on a stained smear. The calculation uses the conventional relation where the volume of fetal whole blood in milliliters equals the fetal cell percent multiplied by 50. Each 300 microgram vial of Rh immune globulin neutralizes approximately 30 milliliters of fetal whole blood or 15 milliliters of fetal red blood cells.

The number of vials is computed by dividing the estimated fetal whole blood volume by 30 milliliters and rounding up to the next whole vial to ensure adequate coverage. Clinicians should interpret results in the clinical context including timing of exposure and prior Rh immune globulin administration. Local laboratory methods and local protocols may vary.

When in doubt consult institutional guidelines or hematology or transfusion services for confirmatory testing and dosing decisions. Reference Kleihauer Betke test and dosing calculations. StatPearls.

Diann M Krywko. Updated 2022. ACOG practice guidance on prevention of Rh D alloimmunization noting that a 300 microgram dose protects against up to 30 milliliters of fetal whole blood.

AABB association bulletin on dosing of Rh immune globulin with similar coverage statements.