Detection and quantitation of fetal maternal hemorrhage utilizing an enzyme-linked antiglobulin test

Existing methods to evaluate fetal-maternal hemorrhage depend upon red blood cell agglutination or blood film elution techniques. These tests are insensitive and difficult to quantitate and reproduce. An enzyme-linked antiglobulin test was evaluated to determine its suitability for clinical testing of postpartum candidates for Rh immune globulin administration. Prepared mixtures of Rh positive fetal and Rh negative adult red blood cells approximating fetal maternal hemorrhage ratios of 0-2.0 percent were studied. In 43 assays, the enzyme-linked antiglobulin test consistently detected Rh positive fetal red blood cells in the 0.5 and 0.25 percent mixtures representing a 25 ml and a 12.5 ml hemorrhage, respectively, in a 70-kg woman. The 0.125 percent red blood cell suspension was positive in 85 percent of the assays and the 0.0625 percent suspension was positive in 56 percent of the tests. Agglutination testing by Du variant technique failed to detect 25 percent of the 0.5 percent mixtures. Only 45 percent of tests with the Rh immune globulin crossmatch detected the 0.5 percent mixture. A modified Kleihauer-Betke procedure was as sensitive, but less reproducible than the enzyme-linked antiglobulin test. Forty-seven Rh immune globulin candidates were studied to assess the quantity of fetal maternal hemorrhage. Fourteen patients (29.8%) had detectable Rh positive red blood cells by enzyme-linked antiglobulin tests but all hemorrhages were less than 12 ml; agglutination tests did not detect any fetal red blood cells. We conclude that the enzyme-linked antiglobulin test is a simple, sensitive, and objective procedure for detecting small amounts of Rh positive red blood cells in Rh negative blood and should be applicable to clinical testing of post-partum Rh immune globulin candidates.