Final answer:
Indicator cells used in the fetal screen method are designed to bind specifically to fetal red blood cells to detect fetal maternal hemorrhage. Similar principles apply in immunochromatographic assays to detect hCG in pregnancy tests.
Step-by-step explanation:
The indicator cells used in the fetal screen method are designed to bind to specific antigens. During a fetal screen, also known as a fetal maternal hemorrhage screen, which is used to determine if there has been any mixing of fetal and maternal blood, the indicator cells bind to fetal red blood cells if they are present in the maternal circulation. Notably, similar principles are used in different types of tests, such as immunochromatographic assays, where in a pregnancy test, for instance, the indicator system would detect the presence of the human chorionic gonadotropin (hCG) antigen with an anti-hCG antibody that is typically conjugated with a colorimetric or fluorescent marker.