Which factors may affect test interpretation for Rhesus (Rh) typing?

Updated: Aug 01, 2018
  • Author: Victoria K Gonsorcik, DO; Chief Editor: Jun Teruya, MD, DSc, FCAP  more...
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Answer

Answer

Factors that can interfere with a type and screen are discussed below.

A history of Rh immunoglobulin (RhoGam/WinRho/Rhophylac) administration can cause interference with a type and screen. Rh immunoglobulin is used mainly in obstetrics to prevent hemolytic disease of the fetus and newborn (HDFN). In theory, the medication is composed of anti-Rh (D) immunoglobulin (Ig) G antibodies that will coat small amounts of exposed fetal red blood cells, which should prevent the mother's immune system from producing anti-D. In subsequent months, up to 6 months after receiving Rh immunoglobulin, the mother's plasma shows the presence of anti-D, which is interpreted as passively acquired anti-D secondary to Rh-immunoglobulin use; thus, there is no clinical concern for hemolysis. The mother still receives Rh-negative blood products if transfusion is indicated.

Another scenario that causes interference with a type and screen is that of an Rh-negative individual who received Rh-positive red cells because of a low inventory of Rh-negative blood; this person will show newly formed anti-D alloantibody. This is a true alloantibody situation and is mainly reserved for Rh-negative males or Rh-negative females beyond childbearing age. The patient should subsequently receive Rh-negative blood products to avoid hemolysis.

False-positive results with Rh typing may result from a positive direct antiglobulin test (DAT) result (coating of red cells with alloantibodies), rouleaux formation (can be seen with patients with multiple myeloma), or contamination, or reagents. False-positive results may also be seen when high-protein Rh reagents that contain 20% protein or other high molecular weight additives are used for typing. Therefore, a proper Rh control reagent should be tested simultaneously before the Rh typing results can be correctly interpreted. [3]

Finally, false-negative results with Rh typing may result from the use of incorrectly diluted red cell suspensions, reagent deterioration, failure to follow the manufacturer's directions, or inappropriate techniques. [3]


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