In plain words
The Kleihauer-Betke test is a lab test on a blood sample from a pregnant person or a new mother. It looks for baby cells in the mother's blood, which show that some of the baby's blood crossed the placenta. This is called . Most of the time the amount is small. The result helps estimate how much Rh medicine is needed after birth or after a bleed, when the mother is and the baby may be Rh positive. Not every hospital uses this test, and newer methods such as flow cytometry are also used. A result is one piece of the picture. Your provider will explain what it means for you and your baby. The test is also used in some cases of or after an injury in pregnancy.
The deeper version
The Kleihauer-Betke acid-elution test relies on fetal resisting acid elution, so fetal red cells stain as ghost cells against adult cells on a peripheral smear. The fraction of fetal cells is multiplied by maternal blood volume to estimate the fetal red cell volume that entered maternal circulation. Flow cytometry is more quantitative and precise at low volumes and is increasingly used. Fetomaternal hemorrhage is reported in a small share of pregnancies, with the largest volumes after , manual placental removal, trauma, and operative birth. ACOG Practice Bulletin 181 (2017) on Rh D alloimmunization gives the rationale for estimating fetal cell volume to guide immune globulin administration after sensitizing events. The controversy concerns accuracy at low volumes and whether routine testing after every birth is needed.
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Sources
- American College of Obstetricians and Gynecologists — Practice Bulletin No. 181: Prevention of Rh D Alloimmunization, 2017
- Kleihauer E, Braun H, Betke K — Demonstration of fetal hemoglobin in erythrocytes of a blood smear. Klinische Wochenschrift, 1957