Ans. is 'c' i.e., Kleinhauser test Kleiheaur betke testo It is quantitative test which is used to calculate the approx volume of the fetal blood entering into the maternal circulation. Based on the principle of acid elution technique and is done by using citric acid phosphate buffer. Fetal red cells (dark refractile bodies) are calculated as per 50 low power fields. If there are 80fetal erythrocytes in 50 low power fields in maternal peripheral blood films, it is estimated as transplacental haemorrhage to the extent of 4 ml of fetal blood.o Though more accurate tests are flow cytometry and immunofluorescence.o Apt test (Singer alkali denaturation test) is another test by which is used to detect the presence of fetal blood in maternal blood. But it is qualitative test. It uses KOH as reagent and is based on alkali denaturation.o Bubble test (shake test) is a bedside test to detect the fetal lung maturity.