Blood Transfusion: Components, Indications, Compatibility and Complications

Blood Transfusion: Components, Indications, Blood Groups, Cross-Matching, Administration and Complications

Study level: Clinical medicine, emergency medicine and pathology | Topic: Hematology and transfusion medicine

Learning objectives

• Describe whole blood, red-cell, platelet, plasma and cryoprecipitate components.
• Choose a component according to the physiologic deficit and indication.
• Explain ABO/Rh compatibility, antibody screening and cross-matching.
• Perform safe bedside administration and monitoring.
• Recognise acute and delayed transfusion reactions and initiate emergency management.
• Apply patient-blood-management principles and know when specialist advice is required.

1. Why transfusions are given

Blood products replace a specific missing function:

Deficit	Preferred component	Purpose
Reduced oxygen-carrying capacity or major red-cell loss	Red-cell concentrate (packed RBCs) or whole blood in selected massive-haemorrhage settings.	Increase haemoglobin and oxygen delivery.
Low platelet number or function with bleeding/procedure risk	Platelet concentrate.	Improve primary haemostasis.
Multiple clotting-factor deficiency with bleeding	Fresh frozen plasma (FFP) or pathogen-reduced plasma.	Replace soluble coagulation factors.
Low fibrinogen	Cryoprecipitate or fibrinogen concentrate according to local availability.	Restore fibrin formation and factor VIII/vWF/factor XIII content.
Specific factor deficiency	Purified factor concentrate or targeted therapy.	More precise replacement with less volume.

Plasma volume alone: crystalloid or balanced resuscitation fluids—not plasma—are usually used for volume replacement when coagulation factors are not deficient.

2. Blood components

2.1 Red-cell concentrate

Red-cell units contain concentrated erythrocytes with most plasma removed. They improve oxygen delivery but do not correct thrombocytopenia or isolated clotting-factor deficiency. Risks include haemolysis, alloimmunisation, circulatory overload, hyperkalaemia, hypothermia and iron accumulation after repeated transfusion.

2.2 Platelets

Platelets may be pooled from whole-blood donations or collected by apheresis. Indications depend on bleeding, procedure risk, platelet function and the cause of thrombocytopenia. Platelet refractoriness can result from HLA antibodies, consumption, sepsis, splenomegaly or nonimmune destruction.

2.3 Plasma

Plasma contains multiple clotting factors and is used for clinically significant bleeding or urgent invasive procedures with documented or strongly suspected factor deficiency. It is not a general “volume expander”; unnecessary plasma exposes patients to allergy, TRALI and circulatory overload.

2.4 Cryoprecipitate/fibrinogen replacement

Cryoprecipitate is rich in fibrinogen, factor VIII, vWF and factor XIII. Use local thresholds and clinical bleeding context. Fibrinogen concentrate offers standardised dosing where available.

2.5 Whole blood

Whole blood provides red cells, plasma and platelets in one unit and may be used in major haemorrhage or resource-limited settings under an approved protocol. Component therapy is usually more targeted and reduces unnecessary exposure.

3. Indications and patient blood management

• Transfuse for active major haemorrhage, symptomatic anaemia with impaired oxygen delivery, or clinically important coagulopathy/thrombocytopenia—not the laboratory value alone.
• Assess haemodynamics, bleeding rate, cardiac/respiratory reserve, pregnancy, sepsis, chronic adaptation and planned procedure.
• Correct reversible causes first when safe: bleeding source, iron/B12/folate deficiency, hypothermia, hypocalcaemia and anticoagulant effect.
• Use a restrictive, single-unit reassessment approach for stable nonbleeding adults where consistent with local guidelines; reassess symptoms and repeat Hb rather than automatically ordering multiple units.
• In massive haemorrhage, activate the local major-haemorrhage protocol early; give balanced red cells, plasma and platelets, monitor calcium/temperature/acid-base and control the source surgically or obstetrically.

4. Blood groups and compatibility

4.1 ABO system

Group	RBC antigen	Plasma antibody	Key rule for red cells
A	A	Anti-B	Can receive A or O RBCs if compatible.
B	B	Anti-A	Can receive B or O RBCs if compatible.
AB	A and B	No anti-A/anti-B	Can receive ABO-compatible RBCs; AB plasma is broadly compatible for plasma donation.
O	No A/B	Anti-A and anti-B	O RBCs can be used in emergencies when group is unknown, subject to local policy; O plasma is not universal.

ABO-incompatible RBCs can cause rapid complement-mediated intravascular haemolysis, shock, kidney injury, DIC and death. Clerical identification errors remain a major preventable cause.

4.2 Rh(D) and other antigens

Rh(D)-negative recipients may form anti-D after exposure through transfusion or pregnancy. Rh matching is especially important for people with pregnancy potential and those requiring repeated transfusion. Other systems—Kell, Kidd, Duffy and MNS—can cause delayed haemolytic reactions and require antigen-negative, phenotype-matched units in selected patients.

5. Pre-transfusion testing

1. Clinical prescription: specify component, indication, urgency, dose/number of units and special requirements (irradiated, leukoreduced, washed, CMV-safe or antigen-negative).
2. Patient identification: use two identifiers; label the blood sample at bedside. A wrong-blood-in-tube error can be fatal.
3. ABO/Rh typing: determine recipient group and confirm historical records.
4. Antibody screen: detect clinically significant unexpected antibodies from previous transfusion or pregnancy.
5. Cross-match: test recipient plasma against donor red cells, electronically or serologically according to laboratory policy.
6. Compatibility report: verify unit number, group, expiry, special processing and visual appearance before release.

If a life-threatening haemorrhage cannot wait, emergency-release blood may be issued under local policy. Obtain a pre-transfusion sample before giving it whenever possible, document the emergency and switch to fully compatible units as soon as testing permits.

6. Special products

Product modification	Why used	Examples/precautions
Leukoreduced	Reduces febrile reactions, CMV transmission risk and HLA alloimmunisation.	Common standard in many services; does not prevent every reaction.
Irradiated	Prevents transfusion-associated GVHD by inactivating donor lymphocytes.	Stem-cell transplant, selected immunodeficiencies and directed donations; follow local indications.
Washed	Removes most plasma proteins.	Recurrent severe allergic reactions or IgA-related anaphylaxis under specialist advice.
CMV-reduced-risk	Reduces transfusion-transmitted CMV risk.	Use according to recipient risk and national policy.
Antigen-negative/phenotype-matched	Prevents alloantibody reactions.	Patients with existing antibodies, chronic transfusion or haemoglobinopathy.

7. Safe bedside administration

1. Confirm consent, indication, allergies, baseline observations and IV access; use a dedicated blood administration set with a filter.
2. At the bedside, independently verify patient identity, unit number, ABO/Rh, cross-match status, expiry, component and special requirements.
3. Inspect the unit for clots, unusual colour, leaks or haemolysis; do not use a damaged or questionable unit.
4. Record temperature, pulse, respiratory rate, blood pressure and oxygen saturation before starting.
5. Begin slowly while observing closely during the initial period; increase only according to patient tolerance and local policy.
6. Recheck observations during and after transfusion; monitor high-risk patients for circulatory overload, respiratory change or pain.
7. Use only approved compatible IV fluid through the line; calcium-containing solutions such as Ringer lactate can interact with citrate in some systems, and medicines should not be mixed in the blood line unless approved.
8. Document component, unit number, start/finish time, observations, response and any reaction.

8. Acute transfusion reactions

Reaction	Timing/features	Mechanism	Immediate action
Acute haemolytic	Minutes to hours: fever, rigors, back/flank pain, chest pain, dyspnoea, hypotension, dark urine, DIC.	Usually ABO incompatibility or other antibody.	Stop transfusion; keep IV with normal saline, recheck identity, notify blood bank, send blood/bag/urine, support shock and renal function.
Febrile non-haemolytic	Temperature rise/rigors without haemolysis; diagnosis of exclusion.	Cytokines or recipient antibodies to donor leukocytes.	Stop and assess; rule out haemolysis/sepsis; antipyretic only after evaluation and according to policy.
Allergic	Itching, urticaria, flushing; severe cases bronchospasm/hypotension.	Reaction to donor plasma proteins.	Stop, assess ABCDE; antihistamine for mild isolated symptoms; treat anaphylaxis with IM adrenaline.
TRALI	Acute hypoxia and noncardiogenic pulmonary oedema within hours.	Donor antibodies or biologic mediators activate recipient neutrophils.	Stop, oxygen/ventilation, avoid unnecessary diuresis, notify blood bank and ICU.
TACO	Dyspnoea, hypertension, pulmonary oedema, raised JVP during/after transfusion.	Volume overload, especially heart/renal failure or rapid infusion.	Stop or slow, sit upright, oxygen and diuresis when appropriate; review future volume/rate.
Septic reaction	High fever, rigors, hypotension, vomiting or shock.	Bacterial contamination, especially platelets.	Stop, cultures from patient and unit, broad antimicrobials and sepsis resuscitation.
Hypotensive reaction	Sudden BP fall without another cause.	Bradykinin or medication interaction; diagnosis of exclusion.	Stop, assess bleeding/anaphylaxis/sepsis and support circulation.

9. Delayed and late complications

• Delayed haemolytic reaction: days to weeks later with falling Hb, jaundice or positive antibody testing from an anamnestic response.
• Alloimmunisation: antibodies against RBC, platelet or HLA antigens complicate future matching and pregnancy.
• Transfusion-transmitted infection: screening lowers risk but cannot make it zero; follow national haemovigilance procedures.
• Iron overload: repeated transfusions deposit iron in liver, heart and endocrine organs; monitor ferritin and organ iron where relevant.
• Transfusion-associated GVHD: donor lymphocytes attack the recipient; often fatal without prevention, hence irradiated products for high-risk patients.
• Post-transfusion purpura: delayed severe thrombocytopenia from platelet alloantibodies.
• Electrolyte/thermal complications: citrate-related hypocalcaemia, hyperkalaemia, hypothermia and acid-base changes during massive transfusion.

10. What to do when a reaction is suspected

1. Stop the transfusion immediately. Do not restart the same unit unless explicitly authorised after evaluation.
2. Assess airway, breathing, circulation, mental state and urine output; call for senior help.
3. Maintain IV access with compatible fluid through a new line if necessary.
4. Recheck patient and unit identification; notify the blood bank and treating clinician.
5. Send the blood bag/tubing, post-reaction EDTA and serum samples, urine and cultures as required.
6. Order CBC, bilirubin, LDH, haptoglobin, creatinine, electrolytes, coagulation tests and DAT when haemolysis is possible.
7. Document, report to haemovigilance and investigate the system error. Treat the physiology—shock, bronchospasm, pulmonary oedema, sepsis or DIC—without delay.

11. Massive transfusion and damage-control principles

• Activate the major-haemorrhage protocol early for uncontrolled bleeding with shock; use balanced components or whole blood according to local protocol.
• Control the source surgically, obstetrically, endoscopically or by interventional radiology; transfusion alone cannot stop bleeding.
• Prevent the lethal triad of hypothermia, acidosis and coagulopathy; warm the patient and products where appropriate.
• Monitor ionised calcium, potassium, pH, temperature, fibrinogen, platelets and coagulation viscoelastic tests if available.
• Reassess frequently; avoid both under-resuscitation and unnecessary exposure.

12. Clinical cases

Case 1: possible ABO reaction

Ten minutes after starting red cells, a patient develops rigors, severe back pain, dyspnoea and hypotension. Stop the transfusion immediately, maintain IV access with compatible fluid, recheck identity, call the blood bank, send reaction samples and treat shock/renal/DIC complications.

Case 2: dyspnoea after transfusion

A patient with heart failure becomes hypertensive and breathless after two units. Consider TACO, but also exclude TRALI, pulmonary embolism, sepsis and acute haemolysis. Assess JVP, chest imaging, oxygenation and cardiac findings; stop/slow transfusion and provide supportive treatment.

Case 3: bleeding after childbirth

In major obstetric haemorrhage, obtain blood before the crisis, activate a major-haemorrhage pathway, use balanced components and treat uterine/placental/surgical causes. Monitor fibrinogen, calcium, temperature and coagulation continuously.

13. Exam-focused comparison

Question	Answer
What is the most dangerous preventable transfusion error?	Wrong patient/wrong blood ABO incompatibility from identification or clerical failure.
Which component treats low fibrinogen?	Cryoprecipitate or fibrinogen concentrate according to local protocol.
TRALI versus TACO?	TRALI is noncardiogenic lung injury with hypoxia; TACO is circulatory volume overload, often hypertension and raised filling pressures.
What is the first action for any suspected reaction?	Stop the transfusion and assess the patient.
Why irradiate selected products?	To prevent donor lymphocytes causing transfusion-associated GVHD.

14. Quick self-test

1. Match red cells, platelets, plasma and cryoprecipitate to their principal deficits.
2. Why is plasma not a routine volume expander?
3. List the steps of pre-transfusion testing.
4. How does ABO-incompatible blood cause shock and renal injury?
5. What are the first six actions in a suspected transfusion reaction?
6. Distinguish TRALI from TACO.

Answers

1. Red cells: oxygen capacity; platelets: primary haemostasis; plasma: multiple clotting factors; cryoprecipitate/fibrinogen: low fibrinogen.
2. It exposes the patient to allergy, TRALI and volume risk without benefit when clotting factors are normal.
3. Clinical order, bedside identification/sample, ABO/Rh, antibody screen, unit selection and cross-match.
4. Recipient anti-A/anti-B antibodies activate complement, causing intravascular haemolysis, hypotension, DIC and acute kidney injury.
5. Stop transfusion, ABCDE, maintain IV access with compatible fluid, recheck identity, notify blood bank/clinician, send samples and treat the physiology.
6. TRALI is acute noncardiogenic pulmonary oedema/hypoxia; TACO is hydrostatic overload with hypertension/raised filling pressures.

Key take-home points

• Transfuse a component for a physiologic deficit, using the smallest effective exposure.
• Correct identification and cross-matching prevent catastrophic ABO reactions.
• Monitor closely at the start and throughout; fever, rash, dyspnoea, pain or hypotension is a reaction until assessed.
• Stop the transfusion first—then diagnose and treat haemolysis, sepsis, anaphylaxis, TRALI, TACO or bleeding.
• Massive transfusion requires source control, balanced components and active prevention of hypothermia, acidosis, hypocalcaemia and coagulopathy.

Selected references

• WHO: Patient blood management and clinical use of blood
• NCBI Bookshelf: Blood Transfusion
• NCBI Bookshelf: Transfusion Reactions
• NCBI Bookshelf: Blood Groups and Red Cell Antigens
• MedlinePlus: Hemolytic transfusion reaction
• WHO: Guidelines and principles for safe blood transfusion practice