Abo blood groups

The ABO blood grouping system is a fundamental classification of human blood types, determined by the presence or absence of specific antigens on red blood cells and antibodies in the plasma. These antigens and antibodies dictate a person's blood type and compatibility for blood transfusion. The ABO system is universally recognized as the most significant system for blood transfusion compatibility.

File:ABO blood type.svg

ABO blood group antigens present on red blood cells and IgM antibodies present in the serum

Understanding Blood Groups

The ABO blood grouping divides blood into four main types, determined by the presence or absence of two main antigens and antibodies. The categorization is as follows:

ABO Group	Blood Type	Antigen A	Antigen B	Anti A antibody	Anti B antibody
A	yes	no	no	yes
B	no	yes	yes	no
O	no	no	yes	yes
AB	yes	yes	no	no

For instance, an individual with the A blood type has A antigens and anti-B antibodies. This system ensures safe blood transfusions, as the recipient's immune system could attack incompatible blood.

Blood Donation Screening

Ensuring the safety of both blood donors and recipients is paramount. Screening procedures are in place to minimize the risk of transfusing infectious diseases.

Donor Evaluation

Before donation, potential donors undergo a questionnaire to assess their eligibility. Those at risk of carrying transmittable diseases or who are unwell are deferred.

Testing Donated Blood

After donation, the blood undergoes multiple tests:

• Blood typing (ABO group)
• Rh typing (positive or negative)
• Screening for infectious pathogens

Infectious Disease Pathogen	Laboratory Tests Used
Bacterial Contamination	Bacterial culture
Hepatitis B virus (HBV)	Hepatitis B surface antigen (HBsAg) detection Hepatitis B core antibody (anti-HBc) detection
Hepatitis C virus (HCV)	Hepatitis C virus antibody (anti-HCV) detection Nucleic acid amplification testing (NAT) for HCV
Human Immunodeficiency virus Types 1 and 2 (HIV)	HIV-1 and HIV-2 antibody (anti-HIV-1 and anti-HIV-2) detection Nucleic acid amplification testing (NAT) for HIV-1
Human T-Lymphotropic Virus Types I and II (HTLV)	HTLV-I and HTLV-II antibody (anti-HTLV-I and anti-HTLV-II) detection
Treponema pallidum (syphilis)	Anti-treponemal antibody detection
West Nile virus (WNV)	Nucleic acid amplification testing (NAT) for WNV

Adverse Reactions to Blood Transfusions

While the risk of an adverse reaction during a blood transfusion is low, it's vital to understand potential complications. Reactions can range from mild allergic responses to severe and life-threatening conditions.

Common Reactions

• Allergic reaction to blood transfusion: Caused by a clash between the transfused allergen and the recipient's pre-existing antibodies.
• Acute hemolytic transfusion reaction (AHTR): Rapid destruction of red blood cells due to receiving an incompatible blood type.
• Delayed hemolytic transfusion reaction (DHTR): The body develops antibodies against transfused red blood cell antigens after 24 hours to 28 days post-transfusion.
• Delayed serologic transfusion reaction (DSTR): New antibodies against red blood cells develop within 24 hours to 28 days post-transfusion without clinical symptoms.
• Febrile non-hemolytic transfusion reaction (FNHTR): Characterized by fever and/or chills without the breakdown of red blood cells.
• Hypotensive transfusion reaction: A drop in blood pressure immediately after starting the transfusion.

Rare Reactions

• Post-transfusion purpura (PTP): Rapid destruction of platelets, leading to a sharp decrease in platelet count.
• Transfusion-associated circulatory overload (TACO): Fluid overload in the recipient's circulatory system.
• Transfusion-related acute lung injury (TRALI): Fluid accumulation in the lungs.
• Transfusion-associated dyspnea (TAD): Respiratory distress post-transfusion.
• Transfusion-associated graft vs. host disease (TAGVHD): Donor T-lymphocytes attack the recipient's cells, causing symptoms such as fever and rash.
• Transfusion-transmitted infection (TTI): Introduction of a pathogen through transfused blood.