What is the potential risk if a Kleihauer-Betke test indicates greater than 15 ml of fetal blood in the maternal circulation?

A Kleihauer-Betke test is utilized to detect the presence of fetal red blood cells in the maternal circulation, which is especially important in the context of Rh incompatibility. If the test reveals greater than 15 ml of fetal blood, it indicates a significant amount of fetal cells entering the maternal bloodstream.

In women who are Rh-negative and carry an Rh-positive fetus, this situation poses a risk for Rh sensitization, which can lead to hemolytic disease of the newborn in subsequent pregnancies. To prevent sensitization, Rh immunoglobulin (Rhogam) is administered; however, the standard 300-mg dose is based on the assumption of a specific volume of fetal blood exposure—typically around 15 ml.

When the test outcome indicates more than 15 ml of fetal blood, it likely means that a higher than usual dosage of Rh immunoglobulin is required to effectively prevent sensitization. Therefore, a standard dose may not be sufficient to counteract the potential for Rh sensitization in this scenario. This underscores the importance of accurately assessing fetal blood volume to determine the appropriate Rh immunoglobulin dosage needed for maternal protection. Consequently, recognizing that the standard dose may fall short is crucial for safeguarding maternal and fetal health.