The rosette test is a sensitive method to detect fetomaternal hemorrhage of 10 cc or more. This qualitative (not quantitative) test will be positive if fetal D-positive cells are present in the maternal sample, indicating a significantly large fetomaternal hemorrhage has occurred. A rosette test may be falsely positive if the mother is positive for the weak D phenotype and falsely negative if the neonate is weak D. If the mother is positive for the weak D phenotype, the rosette test should not be used; instead, a quantitative test such as the Kleihauer-Betke test or flow cytometry should be utilized. If the rosette test is negative, then a dose of 300 micrograms of RhIG is given (sufficient to prevent alloimmunization after delivery in 99% of cases). The RhIG dose suppresses the immune response to up to 30 cc of whole fetal blood (15 cc of red blood cells).If a fetomaternal hemorrhage in excess of 30 cc has occurred, additional testing is mandatory in order to determine the appropriate dosage of RhIG to prevent alloimmunization. A positive rosette test should be followed by a quantitative test such as the Kleihauer-Betke test or an alternative approach such as flow cytometry. See the article on Kleihauer-Betke test for details on how the volume of fetomaternal hemorrhage is calculated. The dosage of RhIG is calculated from the volume of fetal hemorrhage (in mL). Ex: 50 mL fetal hemorrhage / 30 ml = 1.667 (round up to 2) then add 1 = 3 vials of RhIG.