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

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Abstract
Existing methods to evaluate fetal-maternal hemorrhage depend upon red blood cell agglutination or blood film acid 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% 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% mixtures representing a 25-ml and a 12.5-ml hemorrhage, respectively, in a 70-kg woman. The 0.125% red blood cell suspension was positive in 85% of the assays and the 0.0625% suspension was positive in 56% of the tests. Agglutination testing by DU variant technique failed to detect 25% of the 0.5% mixtures. Only 45% of tests with the Rh immune globulin crossmatch detected the 0.5% mixture. A modified Kleihauer-Betke procedure was as sensitive but less reproducible than the enzyme-linked antiglobulin test. Rh immune globulin candidates (47) were studied to assess the quantity of fetal maternal hemorrhage; 14 patients (29.8%) had detectable Rh-positive red blood cells by enzyme-linked antiglobulin tests but all hemorrhages were < 12 ml. Agglutination tests did not detect any fetal red blood cells. 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 postpartum Rh immune globulin candidates.