• Determining the exact number of Rho(D) immune globulin (RhoGAM) vials required for an Rh-negative mother after a massive Fetomaternal Hemorrhage.
• Evaluating trauma, placental abruption, or complicated deliveries in Rh-negative patients.
• Preventing severe alloimmunization (Hemolytic Disease of the Fetus and Newborn) in future pregnancies.

The Kleihauer-Betke test uses acid elution. Adult hemoglobin is soluble in acid; Fetal hemoglobin (HbF) is resistant. The lab counts the number of pink "fetal" cells versus "ghost" maternal cells to generate a percentage.

• To forcefully prevent catastrophic under-dosing, obstetrics uses a unique modified rounding system:
• If the calculation ends in .0 to .4, ROUND DOWN, then ADD ONE VIAL. (e.g., 1.4 -> 1 + 1 = 2 vials).
• If the calculation ends in .5 or higher, ROUND UP, then ADD ONE VIAL. (e.g., 1.6 -> 2 + 1 = 3 vials).
• Flow cytometry is replacing the manual KB test in modern hospitals because manual KB counting is notoriously subjective and error-prone.

• Administer the fully calculated dose of Rho(D) immune globulin within 72 hours of the exposure event.
• If the calculated dose requires 5 or more vials (massive hemorrhage), administer intravenously (Rhophylac) rather than intramuscularly (RhoGAM) due to the sheer volume of fluid.
• Note: Intravenous immune globulin causes rapid fetal RBC destruction. If the mother had a massive hemorrhage, expect a transient drop in her own measured hematocrit as the fetal cells are cleared.

Before the invention of Rho(D) immune globulin in 1968, Rh disease was a leading cause of fetal death and severe neonatal brain damage (kernicterus). The development of this prophylaxis is considered one of the greatest preventive medicine triumphs of the 20th century.