Rh immune globulin: an interfering substance in compatibility testing

Immunoglobulin therapy that interferes with pretransfusion testing may complicate the interpretation of test results and adversely affect patient management. Rh immune globulin (RhIG) should be considered an interfering immunoglobulin therapy when it is detected in an antibody detection test of a sample from a patient who has been treated with RhIG. Frequently, detection occurs in mother's or newborn's plasma. Because an antenatal injection of RhIG is indicated for pregnant Rh-negative women, anti-D is detected frequently by today's highly sensitive antibody screen methods when the mother's plasma is tested subsequently at delivery. Ascertaining the source of anti-D is complicated by the inability of routine clinical laboratory methods to distinguish anti-D due to RhIG from alloimmune anti-D. A combination of qualitative and quantitative test methods, as well as a complete clinical history, is necessary for accurate diagnosis and patient management.