Which of the following tests is used to identify the extent of fetal-maternal hemorrhage?

The Kleihauer-Betke stain is specifically designed to quantify fetal red blood cells in the maternal circulation, which helps identify the extent of fetal-maternal hemorrhage. This test works by determining the presence of fetal cells that can be identified by their resistance to acid or alkali compared to maternal cells. In cases of fetal-maternal hemorrhage, an increased number of fetal red blood cells in the maternal blood can indicate a significant hemorrhage, providing critical information for managing the pregnancy and the health of both the mother and fetus.

The direct antiglobulin test (DAT) is primarily used to detect antibodies bound to red blood cells, which is not specific for assessing fetal-maternal hemorrhage. Flow cytometry can be utilized for various blood analyses, including identifying fetal cells, but it is more complex and not the standard method for estimating the extent of hemorrhage compared to the Kleihauer-Betke test. A crossmatch is essential for ensuring the compatibility of blood transfusions but does not pertain to the evaluation of fetal-maternal hemorrhage.