What lab test is used to detect fetal red cells in maternal circulation?

The Kleinhauer-Betke test is specifically designed to detect fetal red blood cells in maternal circulation, making it the appropriate choice for this question. This test is particularly useful in cases where there may be concerns about fetal-maternal hemorrhage, such as in trauma cases or certain obstetric complications. By quantifying the number of fetal red cells present, healthcare providers can assess the severity of the hemorrhage and determine the need for interventions like Rh immunoglobulin administration in Rh-negative mothers.

The other tests mentioned serve different purposes. Hemoglobin electrophoresis is utilized to identify and differentiate various hemoglobin types, particularly in diagnosing conditions like sickle cell anemia and thalassemia. The Coombs test, which can be direct or indirect, is primarily used to detect hemolytic anemia and assess the presence of antibodies against red blood cells, not specifically to identify fetal cells. Chorionic villus sampling is an invasive prenatal test used to diagnose genetic disorders in the fetus by sampling placental tissue, rather than analyzing maternal blood for fetal red cells.