Introduction to the ABO Blood Group System (Online CE Course)

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Authors: Catherine E. Newkirk, MS, MLS(ASCP) and Janet H. Coggins, MLS(ASCP)SBB
Reviewer: Laurie Bjerklie, MA, MLS(ASCP)CM

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Introduction to ABO Blood Group System is an introductory-level course appropriate for MT and MLT students, pathology residents, or others who need a review of basic biochemistry, genetics, and reactions of the ABO system.

This course can also be used for CLS schools for academic instruction or could be used as a basic orientation for MT and MLT students who are beginning their blood bank rotation during internship.

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Continuing Education Credits

P.A.C.E.® Contact Hours (acceptable for AMT, ASCP, and state recertification): 1 hour(s)
Approved through 7/31/2024
Florida Board of Clinical Laboratory Personnel Credit Hours - General (Blood Banking / Immunohematology): 1 hour(s)
Approved through 7/31/2024


  • Outline the background and development of the ABO system.
  • List antigens and antibodies of the system, including A subgroups.
  • Discuss the inheritance of the ABO antigens, including explanations of genotypes and phenotypes.
  • Discuss development of serum antibodies with respect to "naturally" occurring antibodies and immune antibodies.
  • Determine the ABO blood group, given the forward and reverse typing results.

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(based on 1,280 customer ratings)

Course Outline

Click on the links below to preview selected pages from this course.
  • Introduction to the ABO System
      • Importance of Understanding the ABO System
      • The History of the ABO System
      • The History of the ABO System, continued
      • Table 1: ABO Blood Group System
      • Testing the Patient Red Cells with Known Antisera (Forward Typing)
      • Testing the Patient Serum with Known Red Cells (Reverse Typing)
      • Why does agglutination sometimes occur when red blood cells (RBCs) from one individual are mixed with serum from another?
      • Match the blood types with their corresponding characteristics.
      • True or False: To determine the ABO type, known antisera are mixed with patient RBCs, and known red cells are mixed with patient serum.
  • Development of Serum Antibodies
      • ABO Antibodies
      • Anti-A and Anti-B Development
      • ABO Antibodies and Aging
      • Immune ABO Antibodies
      • Immunoglobulins
      • Which of the following is an event that may produce immune ABO antibodies?
      • Which of the following is the predominant immunoglobulin class for anti-A and anti-B antibodies?
  • Subgroups of A
      • Strength of the A Antigen
      • A1 and A2 Subgroups
      • Rare Subgroups of A
      • Inherited Antigens
      • Significance of A Subgroups For Laboratory Professionals
      • Table 4: Reaction of Red Cell Subgroups with Known Antisera
      • True or False: A1 and A2 individuals cannot be differentiated.
      • Given the results below, what is the most probable ABO type for this individual?Forward (Cell) Grouping Reverse (Serum) Grouping Anti-AAnti-BAnti-A,BA...
      • True or False: The serum of some group A individuals may agglutinate group A1 cells.
  • ABO Typing
  • Genetic Basis for Cellular Antigens
      • Galactose and ABO Antigen Precursor Substance
      • Fucose
      • "A" Antigenic Activity
      • "B" Antigenic Activity
      • The H gene
      • The Bombay Blood Group
      • A, B, and O Genes
      • Diagram of A, B, and O Genes
      • Bombay Blood Group Genes
      • Inherited Genes
      • Deducing the Gene
      • Genotyping
      • Determining Possible Offspring
      • Punnett Squares
      • Which specific terminal sugar causes a red cell to have "A" antigenic activity?
      • Which specific terminal sugar causes a red cell to have "B" antigenic activity?
      • What specific sugar configuration is necessary as a base for the attachment of other sugars?
      • Which of the following phenotypes is not possible in an offspring from an AB and BO mating?
      • What is present in the blood of an individual with the Bombay phenotype that will cause it to agglutinate with any non-Bombay individual's blood?
      • Match the blood types (phenotypes) that will be expressed with the genotypes listed.
  • References
      • References

Additional Information

Level of Instruction: Basic
Intended Audience: Medical laboratory scientists, medical laboratory technicians, and MLS and MLT students as well as pathology residents.
About this Course: This course is part of a series of courses adapted for the web by MediaLab Inc. under license from Educational Materials for Health Professionals Inc. Dayton OH, 45420. Copyright EMHP Inc. 
Reviewer Information: Laurie Bjerklie, MA, MLS(ASCP)CM is currently an Education Developer for MediaLab and LabCE. She earned a B.S. in Medical Laboratory Science from the University of North Dakota and an M.A. in Curriculum and Instruction from Saint Xavier University. She has over 15 years of experience in higher education and has held program director and faculty positions in both MLT and MLS programs.
Course Description: This course explains the basic genetics and principles of the ABO blood group system, as well as the forward and reverse ABO grouping results. Learners will benefit most from this course if they already possess a basic understanding of genetic principles, immune response, the production and structure of antibodies, and antigen-antibody reactions.

How to Subscribe
MLS & MLT Comprehensive CE Package
Includes 180 CE courses, most popular
$109Add to cart
Pick Your Courses
Up to 8 CE hours
$55Add to cart
Individual course$25Add to cart
Gel Card Reaction Grading (2)

Bombay genes