Kleihauer–Betke “KB” test/stain, or Acid elution test, is a blood test used to measure the amount of fetal haemoglobin transferred from a fetus to a mother’s bloodstream.

• Standard method of quantitating fetal-maternal haemorrhage (FMH)
• Performed on Rh-negative mothers to determine the required dose of Rho(D) immune globulin (RhIg) to inhibit formation of Rh-antibodies in the mother and prevent Rh disease in future Rh-positive children.

History

Enno Kleihauer and Klaus Betke described it in 1957.

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Steps

1. Peripheral blood smear is made from the maternal postpartum sample and treated with acid.
   • Fetal cells remain intact because of high concentrations of HbF, while HbA is eluted from the maternal cells.
2. After acid treatment the slides are washed, stained, and examined microscopically.
3. The number of fetal cells (which take up the stain) are counted per number of maternal cells (which appear as ghost cells) to give % fetal cells.
4. The volume of fetal bleed is then calculated to determine how much additional RhIG is required.