RHESUS BLOOD GROUP SYSTEM (Author: Alvine Janse van Rensburg; ND Biomedical Technology-Microbiology, Haematology, Chemistry)

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1 RHESUS BLOOD GROUP SYSTEM (Author: Alvine Janse van Rensburg; ND Biomedical Technology-Microbiology, Haematology, Chemistry) Introduction The term Rh refers to a complex blood group system that comprised up to 50 different antigenic specificities, but the major one is D or Rh 0. Rh positive refers to the presence of the D antigen on the red cells and Rh negative refers to the absence. Rh antigens are highly immunogenic; meaning will elicit antibody response if exposed to D. Transfusion reactions due to Rh antibodies can be severe and Rh haemolytic disease of the newborn can be a heartbreaking experience. History Before 1929 the only significant blood group antigens were those of ABO system, but people were still getting reactions or even die after receiving a compatible blood group. Levine and Stetson described a haemolytic transfusion reaction in an obstetric patient. The baby was stillborn and the father then had to donate blood to the mother, because their ABO blood groups were a match. Then the mother had shown a haemolytic reaction and an antibody was isolated from her blood. It was suggested that the father and baby consist a common factor that the mother lacked. Landsteiner and Wiener then reported on an antibody made by guinea pigs when they were transfused with rhesus monkey red cells. The antibody was named Rh. Nomenclature We will look at 3 theories to better understand the notations used in the Rh system. Fisher-Race This theory involved the presence of 3 separate genes namely D, C and E and their alleles c and e and the absence of D. No d has been found, and is therefore considered a silent allele in the absence of D. The three genes are closely linked on the same chromosome and are inherited as a group of 3. The phenotype (the antigens expressed on the red cell that can detected serologically) of a red cell is defined by the presence or absence of D, C, c, E and e. 1

2 Gene frequency of Rh antigens Gene Frequency D 85% d 15% C 70% c 80% E 30% e 98% Remember, d does not represent an antigen, but simply refers to lack of D. Wiener In contrast, Wiener believed that two genes, one on each chromosome of the pair, control the entire expression of the Rh system in one individual. Multiple alleles exist, the major ones are called R 0, R 1, R 2, R z, r, r, r and r y. Each gene produces a structure on the red cell called an agglutinogen and each agglutinogen can be identified by it factors that react with specific antibodies. The red cell antigens are called Rh 0, rh, rh, hr and hr. If the r is before the h (rh), it refers to uppercase C and E. When the h is before the r, it refers to lower case c and e. Fisher-Race nomenclature may be converted to Wiener and vice versa. The uppercase R indicates D antigen, lowercase r the absence. C is indicated by a one (1) or singe prime ( ). Lowercase c is implied where there is no 1 or indicated. E is indicated by 2 or. Lowercase e is implied where there is no 2 or. When both C and E are uppercase, the letter z or y is used. Fisher-Race Wiener DCe R 1 dce r Dce R 0 DcE R 2 dce r dce r CDE R z CdE r y Rosenfield As the Rh blood group system expanded, it became increasingly difficult to assign names to new antigens. Rosenfield proposed a system that assigns a number to each antigen in order of its discovery. There are no genetic basis, but simply demonstrate presence or absence on the red cell. A minus sign preceding the number demonstrate the absence of that antigen. D is assigned Rh1, C-Rh2, E-Rh3, c-rh4 and e-rh5. So, for example if red cells type positive for DCE, but negative for c and e, the Rosenfield designation is Rh:1,2,3,-4,-5. 2

3 Characteristics of Rh antigens Cell membrane It is believed that the Rh antigens are part of a unit carried on one of the protein molecules embedded in the red cell membrane. These proteins cross the red cell membrane several times, with small loops of the protein on the exterior of the cell membrane. This is sufficient for antigen-antibody interaction. Unlike the ABO system the Rh antigens are not soluble. Weak D The term D u is used to describe some weak reactions with the anti-d reagent. Sometimes testing must be carried through the antiglobulin phase of testing to demonstrate presence of D antigen. The genetic inheritance of these antigens (that are complete but few in numbers) is most frequently seen in the black population. A second mechanism that may result in a weakened expression of D antigen is described as a position effect. The arrangement of C in relation to D appears to interfere with the expression of the D antigen (DCe/dCe). The C in the opposite chromosome suppresses the expression of D. The mosaic D is the third mechanism where one or more parts of the D antigens are missing. Donor blood for transfusion is considered Rh positive if either the D or D u test is positive. If blood types Rh negative, it must be confirmed with an indirect antihuman globulin technique. For transfusion recipients the application of Du is controversial. Because they have the D antigen and cannot make alloanti-d, Rh positive may be transfused. Very rarely the D-mosaic individuals can form alloanti-d when exposed to D-positive red cells. Rh antigen typing The presence or absence of the D antigen is demonstrated by testing the red cells (in suspension) with serum anti-d. A positive reaction is demonstrated by agglutination of the red cells and indicates Rh positive. If negative, it must be confirmed with an indirect antihuman globulin technique. The test is performed with strict adherence to manufacturer s instructions and with the use of positive and negative controls. 3

Causes of false reactions with Rh typing reagents False positive False negative Cold agglutinins Cell suspension too heavy Incubated too long Forget to add reagent Rouleaux Re-suspension too vigorous

4 Causes of false reactions with Rh typing reagents False positive False negative Cold agglutinins Cell suspension too heavy Incubated too long Forget to add reagent Rouleaux Re-suspension too vigorous Fibrin interference Incorrect reagent selected Bacterial contamination Reagent deterioration Incorrect reagent Rh antibodies Unlike the ABO antibodies, most Rh antibodies are IgG and react best at 37 C. They do not occur naturally, but were produced after exposure to foreign red cells, either through pregnancy or transfusion. Exposure to less than 1 ml of Rh-positive red cells can stimulate antibody production. Rh antibodies do no bind complement. Therefore when an Rh antibody coats the red cells intravascularly, complement-mediated haemolysis cannot occur. Haemolysis is usually extravascularly. Because Rh antibodies are usually IgG and because the Rh antigens are well developed early in fetal life; antibodies can cross the placenta of an Rhnegative pregnant female and can coat the fetal red cells. The direct antiglobulin test is positive and this can result in Haemolytic disease of the newborn. Image from (accessed on 2/3/11) To prevent problems due to anti-d: Always give Rh-negative individuals Rh-negative blood Administer Rh immune globulin to Rh-negative mothers to prevent formation of anti-d during pregnancy Transfusion reactions The D antigen is the most immunogenic antigen outside the ABO system. Circulating antibodies appears within 120 days after primary exposure and within 2-7 days after secondary exposure. Rh-mediated transfusion reaction usually results in extravascular haemolysis. The patient may have fever, mild bilirubinaemia, anaemia and a decreased haptoglobin. The direct antiglobulin test is positive and the antibody test may demonstrate circulating antibodies. 4

Haemolytic disease of the newborn (HDN) HDN or erythroblastosis fetalis is a transfusion reaction where Rh-antibodies produced by the mother, cross the placenta and cause destruction of fetal red

5 Haemolytic disease of the newborn (HDN) HDN or erythroblastosis fetalis is a transfusion reaction where Rh-antibodies produced by the mother, cross the placenta and cause destruction of fetal red cells. The mother was sensitized to form antibodies either by previous pregnancies or transfusion, only a small number occurs during pregnancy itself, whereas ABO incompatibility needs no prior stimulus. The incidence of the disease decreased with the introduction of Rh immune globulin (Rhesugam). Image from (accessed on 2/3/11) Blood group antigen-alloantibody implicated: Severe HDN Moderate HDN ABO (<1%) ABO (<10%) Rh-D (20%) Rh-D (30%) Rh-c (7%) Rh-c (23%) K1 (38%) K1 (30%) Fy a (4%) Fy a (2%) The macrophages of the reticuloendothelial system remove the antibodycoated red cells of the fetus. Depending on the amount of antibody, the amount of fetal red cells destroyed can cause anaemia. The fetal bone marrow will produce more red cells, even to a point of releasing immature red cells into the circulation, from there the term erythroblastosis fetalis. In severe cases, the fetus may die in utero. Extramedullary haemopoiesis occurs in the liver and the spleen. The term Hydrops fetalis is used to describe severe edema, effusions (pleural and pericardial) and ascites from the extremely enlarged liver and spleen, casing portal hypertension and liver damage. 5

6 The destruction of red cells continues even after delivery because the antibody persists in the circulation. The haemoglobin from the destroyed red cells is metabolized to bilirubin. During gestation, it crosses the placenta and is eliminated by the mother. After birth, the immature liver of the newborn cannot conjugate this bilirubin efficiently and it can reach levels toxic to the infant s brain. If left untreated, it can cause kernicterus (bilirubin deposit in the basal ganglia) or permanent brain damage. Treatment includes plasma exchange or intravenous immune globulin for the pregnant woman. Intrauterine transfusion can be performed by injecting red blood cells into the umbilical artery. Early delivery to interrupt the crossing of maternal antibody can be considered. After delivery, phototherapy with ultraviolet lights to help with the breakdown of bilirubin can be used. Administration of Rh immune globulin (Rhesugam) as preventative measures occurs at 28 weeks and within 72 hours after delivery or a risk event (abortion, ectopic pregnancy, etc.). Conclusion It is extremely important to correctly assess a patient s ABO and Rh blood group. Transcription errors or failure to perform the Du test may have serious consequences. The recommended obstetric practice is to perform ABO and Rh testing as well as an antibody screen. A follow up might also be a good idea if the Rh was reported as negative. A clinically important anti-d range from 1:8 to 1:32. References Ferreira,M.C. (2009). Postgraduate Diploma in Transfusion Medicine. South Africa. Harmening, D.M. (1983) Modern Blood Banking and Transfusion Practices. Philadelphia. F.A. Davis Company. Rh system. Available from System.htm (accessed on 2/3/11) Stroup,M. & Treacy,M. (1982). Blood group antigens and antibodies. New Jersey. Ortho Diagnostic Systems. 6

The Lecture s topics

The Lecture s topics Blood groups -ABO system *Transfusion reaction -Rhesus factor *Hemolytic disease of newborn Blood transfusion and Tissue transplant The ABO System Discovered in 1901 by Dr. Karl Landsteiner