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Rh blood group system

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The Rh blood group system is a human blood group system, that is the second most important blood group system, after the ABO blood group system. 

 

 

The Rh blood group system consists of 49 defined blood group antigens.

 

 

The five antigens D, C, c, E, and e are the most important blood group antigens.

 

 

There is no d antigen. 

 

 

Rh(D) status is normally described with a positive or negative suffix after the ABO type.

 

 

The terms Rh factor, Rh positive, and Rh negative refer to the Rh(D) antigen only. 

 

 

Antibodies to Rh antigens can be associated with hemolytic transfusion reactions and confer significant risk of hemolytic disease of the fetus and newborn.

 

 

Rh group is a misnomer, actually refers specifically to the Rh D factor.

 

 

The discovery of fetal cell-free DNA in maternal circulation has led to the noninvasive genotyping of fetal Rh genes.

 

 

Rho(D) meaning RhD positive.

 

 

In the United States, approximately 85% of the population has an Rh-positive blood type, leaving 15% with Rh negative. 

 

 

Each person has two Rh factors in their genetics, one from each parent.

 

 

The proteins which carry the Rh antigens are transmembrane proteins.

 

 

The main antigens are D, C, E, c and e.

 

 

The antigens are encoded by two adjacent gene loci, the RHD gene which encodes the RhD protein with the D antigen and the RHCE gene which encodes the RhCE protein with the C, E, c and e antigens.

 

 

The Rh-positive blood cell that make it positive. 

 

 

The antigens that makes the Rh-positive blood cell allows  it to attach to specific antibodies.

 

 

Rh phenotypes are readily identified through the presence or absence of the Rh surface antigens. 

 

 

Most of the Rh phenotypes can be produced by several different Rh genotypes, and the exact genotype can only be identified by DNA analysis. 

 

 

Only the phenotype is usually of any clinical significance to ensure a patient is not exposed to an antigen they are likely to develop antibodies against. 

 

 

R0 (cDe or Dce) is today most common in Africa, particularly in areas below the Sahara. 

 

 

High R0 frequencies characteristic of the ancient Judea Jews, who had emigrated from Egypt prior to their dispersal throughout the Mediterranean Basin and Europe.

 

 

High R0 percentages exist among Sephardi and Ashkenazi Jews compared to native European populations.

 

 

The hemolytic disease of the newborn occurs when there is an incompatibility between the blood types of the mother and fetus. 

 

 

Potential incompatibility if the mother is Rh negative and the father is positive. 

 

 

When any incompatibility is detected, the mother often receives an injection at 28 weeks gestation and at birth to avoid the development of antibodies towards the fetus. 

 

 

The disorder in the fetus due to Rh D incompatibility is known as erythroblastosis fetalis:

 

When caused by the Rh D antigen-antibody incompatibility, 

 

it is called Rh D Hemolytic disease of the newborn or Rh disease. 

 

 

Sensitization to Rh D antigens usually occurs by feto-maternal transfusion during pregnancy may lead to the production of maternal IgG anti-D antibodies which can pass through the placenta. 

 

 

Ru blood group is of particular importance to D negative females at or below childbearing age, because any subsequent pregnancy may be affected by the Rh D hemolytic disease of the newborn if the baby is D positive. 

 

 

Rh disease is preventable by antenatal care with injections of IgG anti-D antibodies (Rho(D) Immune Globulin). 

 

 

The incidence of Rh disease is related to the frequency of D negative individuals in a population: Rh disease is rare in populations of Africa and the eastern half of Asia, and the Indigenous peoples of Oceania and the Americas, and more common in Western European,  Latin Americans and Central Asians.

 

 

Fetal findings in hemolytic disease of the newborn associated with enlarged liver, spleen, or heart and fluid buildup in the fetus’ abdomen seen via ultrasound.

 

 

The worldwide frequency of Rh-positive and Rh-negative blood types is approximately 94% and 6%, respectively. 

 

 

The  population with Rh-negative blood type is set to fall in the future primarily due to low population growth in Europe.

 

 

The frequency of Rh factor blood types and the RhD neg allele gene differs in various world populations.

 

 

If both of a child’s parents are Rh negative, the child will definitely be Rh negative. 

 

 

Otherwise the child may be Rh positive or Rh negative, depending on the parents’ specific genotypes.

 

 

 

The Rh factor inheritance is controlled by two genes, where Rh positive is dominant. 

 

 

The D antigen is inherited as one gene (RHD), on the short arm of the first chromosome, p36.13–p34.3, with various alleles. 

 

 

D− individuals who lack a functional RHD gene do not produce the D antigen, and may be immunized by D+ blood.

 

 

The  next 4 most common Rh antigens, C, c, E and e are expressed on the highly similar RhCE protein that is genetically encoded in the RHCE gene, also found on chromosome 1. 

 

 

The RhD protein, is a membrane transport protein of uncertain and unknown physiological role.

 

 

Studies have reported a protective effect of the RhD-positive phenotype, especially RhD heterozygosity, against the negative effect of latent toxoplasmosis on psychomotor performance.

 

 

A weak D phenotype is characterized by negative reaction with anti-D reagent at immediate spin (IS), and positive reaction at anti-human globulin (AHG) phase. 

 

 

Weak D phenotype can occur because of an altered surface protein that is more common in people of European descent. 

 

 

There is an inheritable form also occurs, as a result of a weakened form of the R0 gene. 

 

 

Weak D patients can receive D positive blood without complications.

 

 

Weak D phenotype is due to a reduced number of D antigens on a red blood cell. 

 

 

Partial D phenotype is due to an alteration in D-epitopes. 

 

 

Partial D patients who are donating blood should be labeled as D-positive.

 

 

Partial D patients receiving blood, they should be labeled as D-negative and receive D-negative units.

 

 

More than 30 different partial D phenotypes have been described.

 

 

Rhnull individuals have no Rh antigens on their red blood cells.

 

 

Very rarely, red blood cells lacking Rh/RhAG proteins have structural abnormalities such as stomatocytosis.

 

 

Red blood cells lacking Rh/RhAG proteins have cell membrane defects that can result in hemolytic anemia.

 

 

Currently, 50 antigens have been described in the Rh group system: D, C, c, E and e antigens are the most important. 

 

 

The other RH antigens are much less frequent or are rarely clinically significant. 

 

 

Rh antibodies are IgG antibodies which are acquired through exposure to Rh-positive blood..

 

 

This occurs generally either through pregnancy or transfusion of blood products.

 

 

The D antigen is the most immunogenic of all the non-ABO antigens. 

 

 

Approximately 80% of D negative patients exposed to a single D-positive unit of blood will produce an anti-D antibody. 

 

 

Alloimmunization is significantly reduced in patients who are actively bleeding.

 

 

 

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