Immunohematology Disorders

Chapter 15 Immunohematology Disorders



I. ABO Blood Group Antigens

A. Definition of ABO blood group antigens

• They are glycoproteins attached to the RBC surface.


B. Blood group O characteristics

1. Most common blood group

• No blood group antigens are present on the RBC membrane.


Blood group O: most common blood group


2. Natural antibodies (isohemagglutinins) in serum

a. Anti-A-IgM, anti-B-IgM

b. Most people have anti-A and B-IgG antibodies.

Group O: anti-A-IgM, anti-B-IgM, anti-A and B-IgG



Blood group antibodies are natural antibodies that are synthesized in Peyer’s patches. A and B antigens that are normally present in food are trapped by specialized epithelial cells called M cells that overlie Peyer’s patches. M cells have close proximity to B lymphocytes lying within the epithelium. M cells transport the A and B antigens to these lymphocytes, resulting in the development of natural antibodies against the antigens. Natural antibodies develop against antigens that are not present on the RBC, which explains why blood group O patients have antibodies against both A and B antigens.




M cells: transport A and B antigens in Peyer’s patches to B lymphocytes


3. Increased incidence of duodenal ulcers

C. Blood group A characteristics

1. Anti-B-IgM antibodies

2. Increased incidence of gastric carcinoma


Group A: anti-B-IgM


D. Blood group B characteristics

• Anti-A-IgM antibodies


Group B: anti-A-IgM


E. Blood group AB characteristics

1. Least common blood group

2. No natural antibodies


Group AB: no natural antibodies


F. Newborns

1. Do not have natural antibodies at birth

Newborns: lack natural antibodies


2. IgG antibodies are of maternal origin.

• IgG antibodies cross the placenta.

G. Elderly people

• Frequently lose their natural antibodies


Elderly people: frequently lose natural antibodies



Elderly patients may not have a hemolytic transfusion reaction if they are transfused with the wrong blood group because they frequently lose their natural antibodies.


H. Paternity issues in newborns

1. Blood group AB parents cannot have an O child.

2. Blood group O parents cannot have an AB, A, or B child.


Blood group AB parents: cannot have O child


3. Blood group A and B parents can have O children if both have AO and BO phenotypes (Fig. 15-1).

image

15-1: Possible children phenotypes if father is BO and mother is AO. See text for discussion.


(Adapted from Goljan EF: Star Series: Pathology. Philadelphia, WB Saunders, 1998.)



Blood group O parents: cannot have AB, A, or B child


I. Determining the ABO group (Fig. 15-2)

1. Forward type

a. Identifies the blood group antigen

image

15-2: Forward and back type to identify ABO blood groups. Forward type identifies the blood group antigen by reacting anti-A and anti-B against patient RBCs. Back type identifies the natural antibodies in the patient serum by reacting A RBCs and B RBCs against the patient serum. Refer to the text for discussion of the blood groups and their natural antibodies.



Forward typing: identifies blood group antigen


• Patient RBCs are added to test tubes that contain either anti-A or anti-B test serum.

b. Example—blood group A RBCs

• Agglutination reaction with anti-A test serum but not with anti-B test serum

2. Back type

a. Identifies the natural antibodies


Back typing: identifies natural antibodies


• Patient serum is added to test tubes containing either A or B test RBCs.

b. Example—blood group A serum

• Patient anti-B-IgM antibodies agglutinate B test RBCs but not A test RBCs.

II. Rh and Non-Rh Antigen Systems

A. Rh antigen system

1. It has three adjoining gene loci.


Five Rh antigens: D, C, c, E, e


a. Locus coding for D antigen (no d antigen)

b. Locus coding for C and c antigen

c. Locus coding for E and e antigen

2. Autosomal codominant inheritance

a. One of the sets of three Rh antigens from each parent is transmitted to each child.

(1) Example—child with cDe from the mother and cde from the father (Fig. 15-3)

• Note that the child lacks E antigen.

(2) Absence of D antigen on a chromosome is designated d even though the antigen does not exist.

b. Possible Rh antigen profiles

(1) DD, Dd, or dd

(2) CC, Cc, or cc

(3) EE, Ee, or ee

3. An individual who is Rh positive is D antigen positive.

image

15-3: Possible Rh phenotypes in children if the father is cde/CDE and the mother is cDE/CDE. See text for discussion.


(Adapted from Goljan EF: Star Series: Pathology. Philadelphia, WB Saunders, 1998.)



Rh positive: D antigen positive


4. Approximately 85% of the population has D antigen.

• Individuals lacking D antigen are considered Rh negative.

5. Rh phenotype of an individual

a. RBCs are reacted with test antisera against each of the Rh antigens.

b. Example—Rh phenotype that is positive for C, c, D, and E antigens but negative for e antigen (phenotype is CcDE)

B. Alloimmunization

Alloimmunization: antibodies develop against foreign antigens


1. Production of an antibody against a foreign antigen not present on an individual’s RBCs


a. Patient exposure to Rh antigen he is lacking (e.g., D antigen)

b. Patient exposure to non-Rh antigen she is lacking (e.g., Kell antigen)

c. These antibodies are called atypical antibodies.

• The individual is considered sensitized if atypical antibodies are present.

2. Significance of atypical antibodies


Atypical antibodies: may produce an HTR


a. May produce a hemolytic transfusion reaction (HTR)

(1) Occurs when blood containing the foreign antigen is infused into an individual

(2) Example—individual with anti-Kell antibodies is exposed to Kell antigen positive RBCs.

(3) IgG antibodies are more likely to produce an HTR than IgM antibodies.

• IgG antibodies react best in warm temperatures, but IgM antibodies react best in cold temperatures.

b. Transfusion requirements in an individual with atypical antibodies

(1) Individual must receive blood that is negative for the foreign antigen.


Individual with an atypical antibody must receive blood lacking the antigen.


(2) Example—individual with anti-Kell antibodies must receive Kell antigen negative blood.

C. Clinically important non-Rh antigens

1. Duffy (Fy) antigens

a. Fy antigens are the binding site for infestation of RBCs by Plasmodium vivax.

b. Majority of blacks lack the Fy antigen.

• Offers protection against contracting P. vivax malaria


Fy antigen negative RBCs: protection against P. vivax malaria


2. I and i antigen systems

a. IgM antibodies (cold agglutinins) may develop against I or i antigen.

b. Increased risk for developing a cold autoimmune hemolytic anemia (refer to Chapter 11)

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Related posts:

  1. White Blood Cell Disorders
  2. Vascular Disorders
  3. Genetic and Developmental Disorders
  4. Red Blood Cell Disorders

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Jun 25, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Immunohematology Disorders

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