Methods for detecting the presence or absence of, and for quantifying, one set of cells in a mixed cell population of at least two sets of cells especially Rh positive cells in a mixed population with Rh negative cells, as is found in a fetal maternal hemorrhage (FMH).;The magnetic particles coated with anti-D antibodies are reacted with the Rh positive fetal cells in Rh negative maternal blood followed by a specific separation and quantifying technique.;Gravitational forces or magnetic forces are used to move reacted magnetic particles to isolate, distinguish and quantify cells differentiated by antigenic composition.;Rh positive cell volume is correlated to the volume of the original blood sample as an indication of the number of doses of RhIG needed to be administered to the mother to prevent subsequent Rh immunization.
