What does the Kleihauer-Betke test detect?

• A. Fetal red blood cells in maternal circulation
• B. Maternal antibodies against fetal cells
• C. Fetal chromosomal anomalies
• D. Placental perfusion

Answer: (A)

Fetal red blood cells in maternal circulation are detected by the Kleihauer-Betke test. The test relies on the difference between fetal hemoglobin (HbF) and adult hemoglobin (HbA): after exposing a blood smear to acid, HbA is eluted from maternal cells while HbF remains inside fetal cells. When the slide is stained, fetal cells stay dark pink/red, whereas maternal cells appear pale, allowing quantification of how much fetal blood has entered the maternal circulation. This measurement helps determine the dose of Rh immune globulin needed to prevent Rh sensitization after delivery or events with bleeding. The test does not assess maternal antibodies directly (that’s done by antibody screens/Coombs testing), nor does it detect fetal chromosomal abnormalities or evaluate placental perfusion.