Detection of fetal hemorrhage in Rh immune globulin candidates. A rosetting technique using enzyme-treated Rh2Rh2 indicator erythrocytes

Current serologic tests occasionally fail to identify women needing more than one vial of Rh immune globulin. We compared the indirect antiglobulin test after incubation with anti-D and a rosetting technique using enzyme treated Rh2Rh2 erythrocytes as methods for identifying significant fetal maternal hemorrhage (FMH). Artificial mixtures containing 0.05 to 1.2 percent Rh1rh (CcDe) fetal red blood cells mixed with rh (ce) adult red blood cells were tested. The indirect antiglobulin test of the 0.6 percent mixture (approximately 30 ml FMH) was reported to be microscopically positive by 17/20 technologists; whereas, 20/20 found the rosetting test to be strongly positive. The volume of FMH in 118 postpartum Rh immune globulin candidates was quantified using Kleihauer's test and formula. The results of the rosetting and Kleihauer tests of blood specimens from these patients were negative 1.4 ml for two, and strongly positive rosetting test and FMH of 6.5 ml for one. The rosetting test utilizes routine blood banking skills and requires 5 minutes more "hands on" time than an indirect antiglobulin test. Confirmation and quantification of positive results by an acid-elution test is necessary.