Blood Groups and Physiological Basis of Blood Transfusion

Introduction

• Blood groups are defined by specific red cell antigens and their corresponding antibodies, forming the basis of safe transfusion.
• Understanding ABO and Rh systems, compatibility testing, and immune reactions is essential to prevent transfusion complications and fetal hemolytic disorders.

Blood Groups

• Human red blood cells contain surface molecules known as blood group antigens, which can trigger immune responses in individuals lacking them.
• In a given individual, antibodies against their own red cell antigens are normally absent. This principle forms the basis of safe blood transfusion.
• Blood group antigens are also termed agglutinogens, while their corresponding antibodies are called agglutinins. Their interaction causes agglutination, or clumping of red blood cells.
• More than 30 blood group systems exist, comprising hundreds of distinct antigens.
• Many systems involve antibodies that react only at low temperatures and are therefore not clinically significant.
• The most important systems for transfusion practice are the ABO system and the Rh system.
• Other clinically relevant systems include MNS, Lewis, Duffy, Kell, P, and Lutheran, which have roles in transfusion medicine and forensic identification.

Uses of Blood Groups

• Blood group typing is essential for safe blood transfusion. It ensures compatibility between donor and recipient and prevents harmful immune reactions.
• Knowledge of ABO system and Rh system allows rapid selection of suitable blood, especially during emergencies.
• Blood group identification is commonly recorded in personal medical records to facilitate urgent transfusion needs.
• Blood group antigens are important in understanding hemolytic disease of the newborn and autoimmune hemolytic anemia. These conditions result from immune reactions against red blood cells.
• Certain blood groups influence susceptibility or resistance to infections. They can affect interactions with parasites, bacteria, and viruses, including those causing malaria.
• Variations or absence of specific red cell antigens may be associated with inherited or acquired disorders. These relationships help in studying disease mechanisms and clinical diagnosis.
• Blood group analysis is widely used in medicolegal investigations. It assists in determining biological relationships, such as disputed parentage, although it is not definitive without genetic testing.
• Some studies suggest associations between blood groups and disease patterns. However, links with personality traits are not scientifically established and should be interpreted cautiously.

Table 16.: Major Blood Group Systems with Associated Genes and Antigen Counts

Blood Group System	Primary Gene(s)	Approximate Number of Antigens
ABO	ABO	4
Rh	RHD, RHCE	45
MNS	GYPA, GYPB	40
P (P1 system)	P1	1
Lutheran	LU	18
Kell	KEL	22
Duffy	FY	6
Kidd	SLC14A1 (formerly HUT11)	3
Lewis	FUT3	3
Lewis-like	Not clearly defined	3
Diego	SLC4A1	7
Cartwright (Yt)	ACHE	2
Xg	XG	1
Li	Not clearly defined	2
Scianna	SC (ERMAP)	3
Dombrock	DO (ART4)	5
Colton	AQP1	3
Landsteiner–Wiener (LW)	LW (ICAM4)	3
Chido–Rodgers	C4A, C4B	9
H	FUT1	1
Kx	XK	1
Gerbich	GYPC	7
Cromer	DAF (CD55)	10
Knops	CR1	5
Indian	CD44	2
Er	Not clearly defined	2

ABO System

• The ABO system is the most important blood group system in transfusion practice due to its highly antigenic A and B antigens.
• Individuals naturally possess antibodies against the antigens absent on their red blood cells.
• This natural antibody formation makes the system physiologically significant.
• Transfusion with incompatible ABO blood leads to rapid agglutination and severe, potentially life-threatening reactions.

ABO Agglutinogens

• The ABO system includes two principal antigens, A antigen and B antigen, present on red blood cells.
• The A antigen has subtypes, mainly A₁ and A₂.
• These antigens are determined by ABO genes located on chromosome 9.

Occurrence

• ABO antigens are expressed on the membrane of red blood cells.
• They are also present in tissues such as salivary glands, lungs, kidneys, pancreas, and testes.
• Small amounts are found in body fluids, including saliva and pancreatic secretions.
• Individuals who secrete H antigen in body fluids are known as secretors.

Time of Appearance

• ABO antigens appear early in fetal life, around the sixth week of development.
• At birth, their expression is low, approximately one-fifth of adult levels.
• Antigen levels gradually increase and reach full expression during adolescence.

Chemical Nature

• A and B antigens are complex oligosaccharides present on red cell membranes.
• They differ in terminal sugar composition: A antigen has N-acetylgalactosamine, while B antigen has galactose.

Blood Groups Based on Antigens

• Blood groups are classified by the presence or absence of A and B antigens on red blood cells.
• Group A has A antigen, and Group B has B antigen.
• Group AB contains both antigens, while Group O lacks both antigens.

Subtypes

• The A antigen has subtypes A₁ and A₂.
• Group A₁ contains both A and A₁ antigens, while Group A₂ contains only A antigen.
• AB group is similarly divided into A₁B and A₂B subtypes.

Distribution

• In the Indian population, approximate frequencies are:
  • Group O: 34%
  • Group B: 31%
  • Group A: 27%
  • Group AB: 8%
• Among Group A individuals, A₁ accounts for about 75%, and A₂ for about 25%.

Role of H Gene and H Antigens

• Formation of A and B antigens depends on the presence of the H gene.
• A basic precursor is first converted into H substance by specific enzymes.
• The A gene and B gene modify H substance into A and B antigens.
• In Group O, A and B genes are absent, so only H substance remains unchanged.
• A, B, and H antigens may also be present in body fluids of secretors, while non-secretors lack them.

Bombay Blood Group

• The Bombay blood group is a rare phenotype in which the H antigen is absent on red blood cells.
• Due to lack of H substance, A and B antigens cannot be formed.
• Routine testing may incorrectly classify these individuals as Group O.
• Their plasma contains anti-A, anti-B, and anti-H antibodies.
• Safe transfusion is possible only with blood from another Bombay phenotype donor.

ABO Agglutinins

• ABO agglutinins include anti-A and anti-B antibodies present in plasma.
• Anti-A antibodies may have subtypes, but all react against A antigen.

Occurrence

• These antibodies are naturally occurring, even without prior antigen exposure.
• They develop in individuals lacking the corresponding A or B antigen on red blood cells.
• The exact mechanism of their formation remains unclear.

Table 16.2: Occurrence of antigens and antibodies in ABO system.

Blood Group	Red Cell Surface Antigens	Plasma Antibodies Present
A	A antigen	Anti-B antibodies
B	B antigen	Anti-A antibodies
AB	Both A and B antigens	No naturally occurring antibodies
O	No A or B antigens	Both Anti-A and Anti-B antibodies

Time and Mechanism of Appearance of Agglutinins

• Anti-A and anti-B antibodies are absent during fetal life and at birth.
• They appear in early neonatal life and gradually increase, reaching peak levels around 10 years of age.

Mechanism of Formation

• The exact mechanism of agglutinin formation is not fully established.
• Environmental antigens from food and intestinal microorganisms resemble A and B antigens.
• These antigens stimulate the immune system to produce corresponding antibodies.
• Low antigen levels and slow antibody production limit significant antigen–antibody reactions.
• Circulating antigens are also removed by phagocytic cells, preventing harmful effects.

Chemical Nature of Agglutinins

• Anti-A and anti-B antibodies are mainly immunoglobulin M (IgM) type proteins.
• They do not cross the placenta due to their large molecular size.
• These antibodies react best at lower temperatures and are termed cold antibodies.

Agglutinins in Different Blood Groups

• Individuals with Group A have anti-B antibodies in plasma.
• Individuals with Group B have anti-A antibodies in plasma.
• Individuals with Group AB lack both anti-A and anti-B antibodies.
• Individuals with Group O possess both anti-A and anti-B antibodies.
• Antibodies are always formed against absent antigens on red blood cells.

Landsteiner’s Law

• If a specific antigen is present on red blood cells, the corresponding antibody is absent in plasma.
• If the antigen is absent, the corresponding antibody is present in plasma.
• This principle applies clearly to the ABO system.
• It does not fully apply to other systems, such as the Rh system, where antibodies are not naturally present.

Antigen and Antibodies for ABO Blood Groups

• Group A has A antigen and anti-B antibodies.
• Group B has B antigen and anti-A antibodies.
• Group AB has both A and B antigens but no antibodies.
• Group O lacks A and B antigens and has both anti-A and anti-B antibodies.

Blood Grouping

• Blood grouping is performed by mixing red blood cells with anti-A and anti-B antisera.
• Agglutination indicates the presence of the corresponding antigen on red cells.
• Absence of clumping indicates absence of that antigen.

Inheritance of ABO Blood Groups

• Blood groups are determined by inherited genes from parents.
• Three main alleles exist: A, B, and O.
• A and B alleles are dominant, while O is recessive.
• Possible genotypes include OO, AO, BO, AA, BB, and AB.
• The observable phenotype depends on the combination of these alleles.
• Individuals with AO show Group A, and BO show Group B.
• If one parent has Group A and the other Group B, the child may have A, B, AB, or O blood group.

Table 16.3: ABO phenotypes and their possible genotypes.

Blood Group (Phenotype)	Possible Genotypes
A	AA or AO
B	BB or BO
AB	AB
O	OO

Rh System

• The Rh system is the second most important blood group system in transfusion medicine.
• It is based on the presence or absence of Rh antigens on red blood cells.
• The most significant antigen is the D antigen.
• Individuals with D antigen are Rh positive, while those without it are Rh negative.
• Rh incompatibility can cause serious transfusion reactions and hemolytic disease of the newborn.

Rh Antigens

• The Rh blood group system includes multiple antigens, primarily C, D, E, c, and e.
• The antigen historically termed d represents the absence of D antigen and is not a distinct antigen.
• There are no naturally occurring antibodies against Rh antigens; antibodies develop only after sensitization (e.g., transfusion or pregnancy).

Key Features

1. The D antigen is the most immunogenic and clinically significant antigen in this system.
2. Based on the presence or absence of D antigen:
   • Rh-positive: D antigen present
   • Rh-negative: D antigen absent
3. Rh antigens are encoded by the RHD and RHCE genes, located on chromosome 1.
4. These antigens are transmembrane proteins that contribute to red cell membrane integrity and are associated with cation transport.
5. Rh antigens are expressed only on red blood cells and are not found in other tissues.

Inheritance of Rh Antigen

• he Rh (D) antigen follows a dominant pattern of inheritance.
• In the Indian population, approximately 95–98% are Rh-positive and 2–5% are Rh-negative.

Genotypes

1. Rh-positive individuals may have:
   • Homozygous (DD) genotype
   • Heterozygous (Dd) genotype
2. Among Rh-positive individuals:
   • Nearly 60% are Dd
   • About 40% are DD
3. Rh-negative individuals have the dd genotype.

Patterns of Inheritance

4. If one parent is homozygous positive (DD) and the other is homozygous negative (dd):
   • All offspring will be heterozygous (Dd) and Rh-positive.
5. If both parents are homozygous negative (dd):
   • All offspring will be dd and Rh-negative.
6. If one parent is heterozygous positive (Dd) and the other is homozygous negative (dd):
   • 50% of offspring will be Dd (Rh-positive)
   • 50% will be dd (Rh-negative).

Rh Antigens

• The Rh system includes several antigens: C, D, E, c, and e.
• The D antigen is the most immunologically significant.
• Individuals are classified as Rh positive if D antigen is present, and Rh negative if absent.
• Rh antigens are membrane proteins found only on red blood cells.
• They contribute to membrane stability and ion transport.
• Genes controlling these antigens, RHD and RHCE, are located on chromosome 1.
• Unlike ABO system, there are no naturally occurring antibodies in the Rh system.

Inheritance of Rh System

• The Rh factor is inherited as a dominant trait.
• Most individuals in the Indian population are Rh positive, while a small percentage are Rh negative.
• Rh positive individuals may be homozygous (DD) or heterozygous (Dd).
• Rh negative individuals have dd genotype.
• If one parent is Rh positive (DD) and the other is Rh negative (dd), all children will be Rh positive (Dd).
• If both parents are Rh negative, all children will be Rh negative.
• If one parent is heterozygous and the other is Rh negative, offspring may be either Rh positive or Rh negative.

Rh Antibody

• The Rh antibody is termed anti-D, produced when an Rh-negative individual is exposed to Rh-positive blood.
• During the first exposure, antibody formation is slow; subsequent exposures produce a rapid and stronger response.
• Anti-D belongs to the IgG class, enabling it to cross the placental barrier.
• Maternal anti-D antibodies can enter the fetal circulation and affect the fetus.
• The antibody shows optimal activity at body temperature (37°C) and is therefore classified as a warm antibody.

Rh Incompatibility

• Incompatibility occurs when an Rh-negative individual is exposed to Rh-positive red blood cells, either by transfusion or pregnancy.

Transfusion Scenario

1. During the first exposure, no immediate reaction occurs because anti-D antibodies are absent.
2. The recipient develops anti-D antibodies over 2–4 months due to immune sensitization.
3. Donor red cells survive for about 120 days, and are usually cleared before antibody levels become significant.
4. The antibodies do not affect the recipient’s own cells, as Rh-negative RBCs lack D antigen.
5. On subsequent exposure, a rapid secondary immune response occurs, leading to hemolytic transfusion reaction.
6. Therefore, an Rh-negative individual may tolerate one Rh-positive transfusion, but repeat exposure is hazardous.

Pregnancy (Hemolytic Disease)

7. In pregnancy, an Rh-negative mother carrying an Rh-positive fetus may become sensitized.
8. The first pregnancy is usually unaffected.
9. In later pregnancies, maternal IgG anti-D antibodies cross the placenta and cause erythroblastosis fetalis (hemolytic disease of the fetus and newborn).

Erythroblastosis Fetalis

Etiopathogenesis

• This condition results from Rh incompatibility, when an Rh-negative mother carries an Rh-positive fetus.
• In the first pregnancy, the fetus is usually unaffected.
• During delivery, small amounts of fetal blood enter maternal circulation, leading to sensitization and production of anti-D (IgG) antibodies.
• In subsequent pregnancies, these IgG antibodies cross the placenta and destroy fetal red blood cells.
• The severity of hemolysis increases in second, third, and later pregnancies.

Clinical Features

• Manifestations arise from hemolysis and anemia:

1. Anemia: Severity depends on the extent of red cell destruction.
2. Hemolytic jaundice: Serum bilirubin may exceed 25 mg% in severe cases.
3. Hydrops fetalis: Generalized edema due to severe anemia and hypoproteinemia.
4. Kernicterus: Deposition of bilirubin in basal ganglia, causing neurological deficits.
   • Occurs because the blood–brain barrier is immature in fetuses and neonates.
5. Extramedullary hemopoiesis: Leads to release of erythroblasts (nucleated RBCs) into circulation, giving the disease its name.

Treatment

• Approximately 50% of affected cases are mild and require no intervention.

1. Intrauterine transfusion: Indicated in severe fetal anemia; commonly performed via the intraperitoneal route.
2. Exchange transfusion:
   • Performed after birth in severe cases.
   • A double-volume exchange (2 × 80 mL/kg) replaces about 90% of blood volume.
   • Blood used should be ABO-compatible, Rh-negative, and cross-matched with maternal blood.
3. Phototherapy: Effective in reducing serum bilirubin levels and preventing complications like kernicterus.

Prevention

• Erythroblastosis fetalis is prevented by administering anti-D (Rh) immunoglobulin.
• A single postpartum dose is given after the first delivery of an Rh-positive infant.
• Antenatal prophylaxis with a small dose during pregnancy provides additional passive immunization.

Other Blood Group Systems

MNS System

• The MNS system was first described in 1927 (MN) and later expanded in 1947 (S antigen).
• It includes M, N, and S antigens.
• These antigens are present on red blood cells and renal capillary endothelium.
• They contribute significantly to the negative surface charge of RBC membranes.
• Common phenotypes include M, N, MN, and S.
• This system is useful in paternity analysis and anthropological genetics.

H System

• The principal antigen is the H antigen, which is a precursor for ABO blood group expression.
• The gene FUT1 (H) is located on chromosome 19.
• The H antigen is present in RBCs, plasma, secretions (saliva, sweat, semen), and epithelial tissues.
• Individuals are classified as secretors or non-secretors based on antigen presence in secretions.
• Blood group O shows maximal expression of H antigen.

Lewis System

• The Lewis system was described in 1946 and includes Leᵃ and Leᵇ antigens.
• These antigens are synthesized in plasma and later adsorbed onto red cells.
• The gene FUT3 (Le) is located on chromosome 19.
• Antigens are also found in body secretions and lymph.
• They act as receptors for Helicobacter pylori.
• Antibodies are IgM type, do not cross the placenta, and do not cause hemolytic disease of the newborn.

Ii System

• The Ii system was identified in 1956 and includes I and i antigens.
• These antigens are present in RBCs, plasma, lymph, and secretions.
• At birth, i antigen predominates, while I antigen is poorly developed.
• A gradual conversion from i to I antigen occurs within the first 2 years of life.
• In hemoglobinopathies, increased expression of i antigen may persist.

Pl System

• The P system was first described in 1927.
• It includes P1, P, and Pk antigens.
• The genes are located on chromosome 22.
• These antigens are found in RBCs, platelets, lymph, and fibroblasts.
• The P1 antigen has associations with certain parasitic infections.

Duffy System

• The Duffy system was described in 1950 and includes Fyᵃ, Fyᵇ, and Fy3 antigens.
• The FY gene is located on chromosome 1.
• These antigens function as receptors for chemokines (e.g., IL-8).
• Fyᵃ and Fyᵇ facilitate entry of Plasmodium vivax into RBCs.
• The Fy(a−b−) phenotype confers resistance to vivax malaria.

Kidd System

• The Kidd system was identified in 1951.
• It includes Jkᵃ, Jkᵇ, and Jk3 antigens.
• The JK (SLC14A1/HUT11) gene is located on chromosome 18.
• These antigens are restricted to the red cell membrane.
• They are associated with delayed hemolytic transfusion reactions.

Kell System

• The Kell system was described in 1946.
• Major antigens include K, k, Kpᵃ, and Kpᵇ.
• Genes involved are KEL (chromosome 7) and XK (X chromosome).
• Expression occurs in RBCs, bone marrow, and fetal liver (KEL), and in muscle and neural tissues (XK).
• The K antigen is highly immunogenic and clinically important in transfusion practice.

Lutheran Blood Group System

• The Lutheran system includes Luᵃ, Luᵇ, and Lu3 antigens.
• These are encoded by the LU gene on chromosome 19.
• Antigens are expressed on RBCs, as well as in brain and placenta.
• They play roles in cell adhesion, receptor interactions, and tissue organization.

Table 16.4: Blood group-associated diseases

Category	Blood Group / Antigen	Associated Conditions
Disease Predisposition	A	Gastrointestinal and gynecological cancers; pernicious anemia; thrombotic disorders; immune thrombocytopenia
	B	Increased susceptibility to urinary tract infections and gonorrhea
	O	Peptic ulcer, rheumatoid arthritis, typhoid fever, von Willebrand disease
	Other antigens (Le, Fy, K, Rh−, Ii)	Autoimmune, infectious, and hematologic disorders including malaria, hemolytic anemia, and hemoglobinopathies
Disease Resistance	P1/Pk, Duffy (Fy)	Protection against E. coli pyelonephritis and reduced invasion by Plasmodium vivax
Antigen Absence	Rhnull, Kx	Rare syndromes with hemolysis and abnormal red cell morphology
Antigen Alteration	Weak or Acquired A, B, Rh, K, MN, Jk	Seen in leukemia, infections, and gastrointestinal pathology

Blood Group-associated Diseases

• Certain disorders show variation in frequency among specific blood groups.
• Some conditions arise due to absence or structural alteration of blood group antigens.
• These associations are clinically relevant for disease risk assessment and research.

Physiological Basis Of Blood Transfusion

• Blood transfusion involves administration of whole blood or its components.
• It is essential in acute hemorrhage and severe anemia.
• Repeated transfusion carries risks of infection transmission and immunological complications.

Indications for Transfusion

1. Acute blood loss: Whole blood is preferred to restore circulating volume and oxygen-carrying capacity.
2. Chronic anemia: Packed red cells are used to improve hemoglobin concentration without excess volume.
3. Bone marrow failure: Conditions such as leukemia and aplastic anemia require component therapy, including red cells and granulocytes, to manage anemia and infection risk.
4. Purpura: Platelet transfusion is indicated to correct thrombocytopenia and prevent bleeding.
5. Clotting factor deficiencies: Fresh frozen plasma is administered. In hemophilia, cryoprecipitate provides factor VIII and fibrinogen.
6. Surgical management: Transfusion is given before or during surgery if anemia is present or significant blood loss is expected. Loss of moderate blood volume may be tolerated in stable individuals.
7. Burns: Loss of plasma proteins is corrected with plasma or colloids. Packed red cells are added if severe anemia develops.
8. Hemoglobinopathies: Regular transfusion is essential in disorders such as thalassemia and sickle cell disease to maintain hemoglobin levels and suppress abnormal erythropoiesis. Repeated transfusion may cause iron overload, requiring monitoring and management.

Procedure of Blood Transfusion

• Select a medically fit and compatible donor after proper screening.
• Perform ABO and Rh typing for both donor and recipient.
• Conduct cross-matching to confirm compatibility and prevent adverse reactions.
• Carry out antibody screening to detect clinically significant antibodies in the recipient.
• Avoid incompatible transfusion, as it can cause agglutination and acute hemolysis.
• Ensure all compatibility tests are completed before transfusion to maintain patient safety.

Selection of Appropriate Donor

1. Select a healthy donor free from transfusion-transmissible infections.
2. Ensure donor age is between 18 and 60 years with voluntary consent.
3. Confirm adequate hemoglobin level before donation.
4. Screen for infections such as human immunodeficiency virus, hepatitis, and malaria.
5. Exclude individuals with systemic diseases to ensure recipient safety.

ABO and Rh Typing

• ABO and Rh systems are essential for safe blood transfusion.
• ABO incompatibility can cause rapid and severe hemolytic reactions.
• Rh incompatibility usually produces delayed immune responses.
• Therefore, strict compatibility testing is required before transfusion.

Universal Donor

• Individuals with O negative blood group are considered universal donors.
• Their red cells lack A, B, and Rh antigens.
• This reduces the risk of agglutination in recipients.
• However, compatibility testing is still necessary for safe transfusion.

Universal Recipient

• Individuals with AB positive blood group are considered universal recipients.
• Their plasma lacks antibodies against A, B, and Rh antigens.
• This prevents agglutination reactions during transfusion.
• They can receive red cells from all ABO and Rh blood groups.
• However, proper compatibility testing is still required for safe transfusion.

Cross-matching

• Cross-matching is performed to ensure blood compatibility before transfusion.
• Two types are recognized: major and minor cross-matching.

Major Cross-matching

• Donor red blood cells are tested against recipient plasma.
• This detects harmful antibodies present in the recipient’s plasma.
• ABO antigens are highly immunogenic and can cause strong agglutination even in small amounts.
• Incompatible reactions may occur despite fewer donor cells.
• Donor antibodies are usually diluted in recipient plasma and are less significant.
• Therefore, matching donor red cell antigens with recipient plasma antibodies is critical.
• This step helps prevent hemolysis and serious transfusion reactions.

Minor Cross-matching

• Donor plasma is tested against recipient red blood cells.
• It evaluates antibodies in donor plasma that may react with recipient cells.
• This test is less critical because donor plasma is diluted after transfusion.
• Dilution reduces antibody concentration, lowering the risk of hemolysis.
• Significant reactions are therefore uncommon.
• However, it is still performed to ensure complete compatibility and transfusion safety.

Antibody Screening of the Patient

• Recipient serum is screened for clinically significant antibodies.
• It helps detect autoantibodies or alloantibodies that may destroy donor red cells.
• This step reduces the risk of hemolytic transfusion reactions.

Blood Collection and Storage

Collection of Blood

Collection of Blood

1. Blood is collected by venipuncture, commonly from the antecubital vein.
2. Approximately 350 milliliters of blood is obtained from a single donor per session.
3. Blood is collected into sterile bags containing anticoagulant such as citrate–phosphate–dextrose.
4. The anticoagulant maintains appropriate pH and preserves red cell viability.
5. Collection usually takes 7 to 10 minutes under controlled conditions.

Donor Monitoring and Care                                                

1. Vital signs, including blood pressure and heart rate, are assessed after donation.
2. Temporary effects such as sweating, dizziness, or mild cardiovascular changes may occur.
3. Donors should rest adequately and avoid strenuous activity for the remainder of the day.
4. A minimum interval of three months is recommended between donations to ensure recovery.

Autologous Donor Blood

• Autologous transfusion uses the patient’s own blood for later transfusion.
• It is commonly planned before elective surgical procedures.
• The patient’s hemoglobin level should exceed 12.5 g% before donation.
• Blood can be collected at intervals of about 72 hours, ensuring hemoglobin remains above safe limits >11 g%.
• Typically, 2 to 4 units of blood of 250 ml each can be collected and stored for use during surgery.
• This approach reduces risks of infection transmission and immune reactions.

Storage of Blood

• Blood is preserved in blood banks at 4 degrees Celsius.
• It should preferably be used within two weeks to maintain cell viability.
• Prolonged storage increases risk of hemolysis and reduced effectiveness.
• Blood stored beyond three weeks is generally unsuitable for transfusion.

Red Cell Changes during Storage

• Red blood cells show progressive biochemical and structural changes during storage in citrate solutions at 4°C due to reduced metabolism.

1. Ionic imbalance occurs, with increased intracellular Na⁺ and decreased K⁺, due to reduced Na⁺–K⁺ pump activity. This leads to water entry and cell swelling.
2. Cells become swollen and spherocytic, increasing the risk of spontaneous hemolysis.
3. Leukocytes and platelets largely disappear within 24–48 hours of storage.
4. ATP levels decrease, while inorganic phosphate increases, reflecting impaired cellular energy metabolism.

Red Cell Changes during Storage

• Red cells show metabolic decline during storage at low temperature.
• Reduced sodium–potassium pump activity alters ion balance.
• Intracellular sodium increases, while potassium decreases.
• Water enters cells, causing swelling and increased fragility.
• Cells become spherical and prone to hemolysis.
• Adenosine triphosphate levels decrease, impairing cellular functions.
• Inorganic phosphate levels increase due to metabolic imbalance.
• Leucocytes and platelets rapidly deteriorate within 24 to 48 hours.

Changes in Stored Blood after Transfusion

• After transfusion, red cell metabolism increases markedly within 24 hours.
• Sodium (Na⁺) is expelled from cells, and potassium (K⁺) re-enters, restoring ionic balance.
• The volume, shape, and membrane fragility of red cells return to near normal within 24–48 hours.
• Approximately 80% of transfused RBCs survive at 24 hours if blood is used within 14 days of storage.
• Cell survival declines significantly when storage exceeds 2 weeks (14 days).
• Blood is ideally used within 14 days, acceptable up to 21 days, and should not be used after 30 days.

Hazards of Blood Transfusion

• Blood transfusion carries inherent risks, even under optimal conditions, and many reactions result from human error.

I. Mismatched Transfusion

• Incompatible transfusion causes acute hemolytic reactions, usually due to ABO incompatibility.
• Donor RBCs undergo agglutination and hemolysis.
• Clinical effects include fever, shivering, hemoglobinemia, hemoglobinuria, and jaundice.
• Acute renal failure may occur due to tubular obstruction, vasoconstriction, and shock.
• Hyperkalemia from RBC lysis may lead to cardiac arrest.

II. Faulty Transfusion Technique

• Thrombophlebitis may occur, especially with repeated transfusions.
• Air embolism can obstruct pulmonary circulation; risk is reduced with plastic blood bags.

III. Massive Transfusion

• Defined as >10 units within 24 hours or replacement of total blood volume.
• Leads to circulatory overload, arrhythmias, and hyperkalemia.

IV. Other Reactions

• Febrile reactions occur due to pyrogens.
• Allergic reactions cause itching, erythema, or anaphylaxis.

V. Transmission of Diseases

• Transfusion may transmit hepatitis, malaria, AIDS, and syphilis.