Rh Phenotyping Objectives

Exercise 4 Laboratory Procedure Manual

Rh Phenotyping

Objectives:

1. List 4 reasons for determining an individuals’ Rh phenotype.

2. State the antigens of the Rh blood group system.

3. Define the following terms: “dominant, codominant, heterozygous, and homozygous as they relate to inheritance of the Rh antigens.

5. Define the terms “phenotype” and “genotype” as they relate to blood group antigens.

6. Briefly state the procedure whereby an individual’s Rh phenotype is determined.

7. Recall each of the Rh genes in both Fisher-Race and Wiener notation.

8. Given an Rh phenotype, list the potential genotypes in both Wiener and Fisher-Race notations.

10. Determine the Rh phenotype and probable genotype of two (2) patient samples.
Discussion

In this procedure, commonly tested antigens of the Rh system will be studied. Normally the only Rh antigen identified in routine pretransfusion testing is the D antigen. Four additional Rh antigens which may be tested for are C, E, c, and e. Phenotyping for these antigens may be useful in family studies, resolution of antibody problems, population studies, cases of disputed parentage, and to predict whether the sexual partner of a woman with Rh antibodies is likely to transmit genes that will result in offspring negative for the particular antigen.

The Rh system initially appears simple and straightforward since it involves only five (5) antigens (C, c, E, e, and D), but it is in fact one of the more complicated human blood group systems known. The gene complex is inherited and individuals may be analyzed in terms of separate antigens: D or its absence, C or c, and E or e.
The two genes (RHD and RHCE) are in close proximity of each other on the chromosome. RHD encodes for the D antigen and the other gene encodes for the CE antigens in various combinations (ce, cE, Ce, or CE). Most D-negative phenotypes are the result of the complete deletion of the RHD gene.
The alleles C and c, and E and e are codominant; therefore, if both alleles are present (one from each parent) both will be expressed.
Wiener theorized that the Rh antigens displayed by an individual are the result of only a pair of genes, one inherited from each parent. If these are identical, the individual is homozygous for that gene and all the products of the gene will be expressed in a double dose on the person's red cell. When the genes inherited from each parent are not identical, the person is heterozygous for two different genes and, since the Rh genes are codominant, the products of both will be expressed on the person's red cells. Antigens that are products of both genes will be present in double dose, while those produced by only one of the pair of genes will be present in single dose.
EXAMPLE:

DCe/DCE (slash separates the gene) transmitted from each parent

Antigen D = homozygous, present on both sides

Antigen C = homozygous, present on both sides

Antigens E and e = heterozygous, each one present on one side only
A phenotype is the assortment of antigens actually detectable on an individual's red cells using selected antiserums. In many blood group systems, the phenotype is an exact expression of the genotype. Unfortunately, this is not the case in the Rh system. Since any one antigen may derive from any of several genes, identifying antigens does not always allow the genotype to be deduced with certainty. Presumptions regarding the most probable genotype rest on knowledge of the frequency with which particular antigenic combinations derive from a single gene complex. To determine the genotype with more certainty, it is necessary to do family studies which are not always possible. The following is an example of a phenotype and the possible genotypes which could be present.
EXAMPLE:

Phenotype (antigens detected on the red cells) is: D, C, c, e

Possible Genotypes-Fisher-Race	Possible Genotypes-Wiener
DCe/ce	R^1/r
DCe/ce	R^1R^0
Dce/Ce	R^0r’

In the general population, the most common D positive genotype is R1/r. The most common D negative genotype is rr.

Principle

The Rh phenotype is determined by testing the patient red blood cells with the five standard antiserums: anti-D, anti-C, anti-c, anti-E, and anti-e. If the antigen to which the antiserum is directed is present, agglutination of the red blood cells will occur. No agglutination of the red blood cells indicates the absence of the antigen. Based on the reactions with these serums, certain statistical assumptions are made, not always correctly. For instance, if a cell reacts with anti-C but not with anti-c, the antigen C is assumed to be present in a double dose (homozygous for C). The exceptions to this are rare, but may be significant in paternity testing.

In the past, the reagent antiserums were made from individuals who have developed an antibody against a specific blood group antigen. Although human source anti-serums are still available, the move is to provide these reagents from clones.
Agglutination of an individual's red cells by a specific antiserum indicates the presence of the corresponding antigen. No agglutination indicates its absence.


Reagents

1. Blood Bank Reagent Rack

2. Anti-C, Anti-E, Anti-c, Anti-e, Rh control

3. Blood Bank plastic pipets

4. Blotting squares (Biowipes)

5. 12x75 test tubes

6. Serofuge

7. Heat Block

8. Agglutination viewer

9. Squirt bottle of 0.85% saline

10. Sharpie

*The instructor will explain and demonstrate the controls that are performed for the Rh system testing.

ABO/D Procedure

1. 
   Refer to laboratory three for the ABO/D typing laboratory and perform an ABO/D type on the patient. Perform the Rh control with the ABO/D as a patient control for all of the antisera testing.
   
2. 
   Review the results with your instructor before performing the Rh system typing procedure.
   

Rh System Typing Procedure

1. 
   Label a tube for the each Rh typing sera with the patient's first and last initial and the Rh anti-sera to be tested: Anti-E, Anti-e, Anti-C and Anti-c.
   
2. 
   CAREFULLY place one drop of the correct typing sera into each of the properly labeled tubes.
   
3. 
   Anti-c
   
   1. 
      Place one (1) drop of the 3-5% patient cell suspension in the tube labeled Anti-c.
      
   2. 
      Mix the contents of the tube thoroughly and incubate for 5 minutes at 37C.
      
   3. 
      Centrifuge 15-20 seconds.
      
   4. 
      Read macroscopically and record results.
      
   5. 
      Incubate a negative test for 10 minutes at 37C.
      
   6. 
      Centrifuge 15-20 seconds.
      
   7. 
      Read macroscopically and record results.
      
4. 
   Anti-E, Anti-e, and Anti-C
   
   1. 
      Place one (1) drop of the 3-5% patient cell suspension in each of the tubes labeled
      Anti-E, Anti-e, and Anti-C.
      
   2. 
      Mix the contents of the tube thoroughly.
      
   3. 
      Centrifuge for 15-20 seconds.
      
   4. 
      Resuspend the red blood cells by gently shaking and examine for macroscopic agglutination.
      
   5. 
      Record results.
      
   6. 
      If the test is negative or shows doubtful agglutination, incubate the test mixture at room temperature (23 +/- 3C) for 15 minutes.
      
   7. 
      Centrifuge for 15-20 seconds.
      
   8. 
      Read macroscopically and record results.
      
5. 
   Confirm the Rh typing results with your instructor.
   
6. 
   Determine the individual’s phenotype and most probably genotype in the appropriate space provided on the results page. Use the attached chart to assist in the determination of the most probably genotype.
   

Interpretation of Results

Once the results of antigen typing have been obtained, the most probable genotype must be determined. At first this will be confusing and difficult, but interpretation will get easier with practice. The following example may help.

Results obtained:

Anti-D	Anti-C	Anti-c	Anti-E	Anti-e
4+	4+	4+	0	4+

Positive reactions indicate the presence of the antigen; negative reactions indicate the absence of the antigen. The phenotype of this patient (antigens detectable on the RBC) is D, C, c, and e.

An Rh gene complex consists of a D, C or c, E or e antigens inherited from each parent. When a patient is D positive the phenotype of the person is either heterozygous or homozygous for D. Make

a separate column for each possible genotype, the other Rh antigens will be added to this “base” type.

Heterozygous D Homozygous D

D / D /D
The results from the Rh phenotype indicates that the patient is C+ and c+, the individual is heterozygous for the C antigen, so place a C or c on either side of the homozygous or heterozygous D. It is critical to remember to list ALL possible combinations.

Combinations

DC /c

Dc /C

DC /Dc
The next antigen to “plug in” is E. The patient is E neg and e+ indicating that this individual is homozygous for e, so e will be present on both sides.

Combinations

DCe/ce

Dce/Ce

DCe/Dce
You must now convert the Fisher-Race notations to Wiener using the chart supplied; also indicate the frequencies in which these genotypes occur:

Combinations Wiener Frequency

DCe/ce R¹r 33%

Dce/Ce R⁰r’ <0.1%

DCe/Dce R¹R⁰ 2%

One thing to remember is that frequencies given are for the white population. In the black population the R⁰ genotype is very common. It is critical to know the race of the individual when determining most probable genotypes.
Interpreting Results

Memorize this chart!

Antigens	Fisher-Race	Wiener
D,c,e	Dce	R^0
D,C,e	DCe	R^1
DcE	DcE	R^2
D,C,E	DCE	R^z
ce	ce	r
Ce	Ce	r’
c,E	cE	r”
C,E	CE	r^y

In interpreting reactions for genotypes, always remember that if the D antigen is present it does not mean that it is homozygous. Figure the genotype with D on one side and no D on the other (heterozygous for D). Use the chart on the following page and select the genotype with the highest frequency. For example, if the D, C, c, and e antigens are present, there are three (3) possible genotypes:

Combinations Wiener Frequency

DCe/ce R¹r 33%

DCe/Dce R¹R⁰ 2%

Dce/Ce R⁰r’ 0.01-0.1%

The most probable genotype is R1r since this has the highest statistical probability.

Rh Genotypes and Their Serological Reactions

Genotypes		Reactions with anti-					Caucasian frequency (%)
Fisher-Race	Wiener	D	C	E	C	e
DCe/ce	R^1r	+	+	0	+	+	33
DCe/Dce	R^1R^0	+	+	0	+	+	2
Dce/Ce	R^0r’	+	+	0	+	+	**
DCe/DCe	R^1 R^1	+	+	0	0	+	18
DCe/Ce	R^1r’	+	+	0	0	+	*
DcE/ce	R^2r	+	0	+	+	+	11
Dce/cE	R^0r”	+	0	+	+	+	**
DcE/Dce	R^2 R^0	+	0	+	+	+	*
DcE/DcE	R^2 R^2	+	0	+	+	0	2
DcE/cE	R^2r”	+	0	+	+	0	*
DCe/DcE	R^1 R^2	+	+	+	+	+	12
DCe/CE	R^1r^y	+	+	+	0	+	¥
DCe/cE	R^1r”	+	+	+	+	+	1
DcE/CE	R^2r^y	+	+	+	+	0	¥
DcE/Ce	R^2r’	+	+	+	+	+	*
DCE/DCE	R^zR^z	+	+	+	0	0	¥
DCE/DCe	R^z R^1	+	+	+	0	+	*
DCE/DcE	R^z R^2	+	+	+	+	0	**
DCE/Ce	R^zr’	+	+	+	0	+	¥
DCE/Dce	R^z R^0	+	+	+	+	+	**
DCE/cE	R^zr”	+	+	+	+	0	¥
DCE/ce	R^zr	+	+	+	+	+	*
DCE/CE	R^zr^y	+	+	+	0	0	¥
Dce/CE	R^0r^y	+	+	+	+	+	¥
Dce/ce	R^0r	+	0	0	+	+	2
Dce/Dce	R^0R^0	+	0	0	+	+	**
Ce/ce	r’r	0	+	0	+	+	*
Ce/Ce	r’r’	0	+	0	0	+	¥
cE/ce	r”r	0	0	+	+	+	*
cE/cE	r”r”	0	0	+	+	0	**
Ce/cE	r’r”	0	+	+	+	+	**
CE/ce	r^yr	0	+	+	+	+	¥
CE/cE	r^yr”	0	+	+	+	0	¥
CE/Ce	r^yr’	0	+	+	0	+	¥
CE/CE	r^yr^y	0	+	+	0	0	¥
ce/ce	rr	0	0	0	+	+	15

* = less than 1 percent but greater than 0.1 percent

**=less than 0.1 percent but greater than 0.01 percent

¥ =less than 0.01 percent
Name: ____________________________________________
Rh Phenotyping

Study Questions

1. 
   List the antigens of the Rh system. (2.5 points)
   

2. 
   State three situations in which testing for the Rh antigens (phenotyping provides useful information. (1.5 points)
   
   1. 
      
      
   2. 
      
      
   3. 
      
      

3. 
   What does it mean to state that the Rh antigens C and c or E and e are “codominant”? (1 point)
   

4. 
   Define homozygous. (1 point)
   

5. 
   Define heterozygous. (1 point)
   

6. 
   Define genotype. (1 point)
   

7. 
   Define phenotype. (1 point)
   

8. 
   State the most common D positive genotype in both Fisher-Race and Wiener notations. Provide the same for most common D negative genotype. (2 points)
   

	Fisher-Race	Wiener
D positive
D negative

9. 
   How are presumptions regarding the most probable genotype determined? (1 point)
   

10. 
    Fill in the following chart and memorize. (8 points)
    

Fisher-Race	Wiener
a.	R^1
DcE	b.
c.	R^z
ce	d.
e.	R^0
cE	f.
g.	r’
ce	h.

11. 
    For the following phenotypes list all possible genotypes. State each ones’ statistical probability as given for Caucasians (use Fisher-Race and Wiener). Circle the most probably genotype. Point values vary.
    
    1. 
       D, C, E, e (3 points)
       

2. 
   c, e (1 point)
   

3. 
   D, E, c, e (3 points)
   

12. 
    State two situations in which a D control must be run and the reason for running it. (2 points)
    

Rh phenotyping (rev. 2/2015)