Unit 2: Compatibility testing and transfusion complications
Blood Banking notes · PTU syllabus (BMLS603-18)
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Unit summary
Compatibility testing prevents transfusion reactions. This unit covers collection of samples for cross-matching, major and minor cross-matching, enzymes in the blood bank, hazards and complications of transfusion, investigation of reactions and mismatched transfusion, and direct and indirect Coombs tests.
After this unit you can
- Perform major and minor cross-matching
- Use enzymes and antiglobulin tests
- Describe complications of transfusion
- Investigate a transfusion reaction
PTU syllabus topics
- Compatibility testing — collection for cross-matching
- major and minor cross matching
- use of enzymes (papain) in the blood bank
- complications and hazards of transfusion
- investigation of transfusion reactions and mismatched transfusion
- direct and indirect Coombs tests
Detects
Antibodies already on red cells
Free antibodies in serum
Sample
Patient's red cells
Patient's serum + reagent red cells
Used for
Haemolytic disease of newborn, transfusion reaction, autoimmune haemolysis
Cross-matching, antibody screening in pregnancy
Topic 1
Sample collection for cross-matching
- Patient sample (clotted or EDTA) taken within 3 days of transfusion if the patient was recently transfused or pregnant; two identifiers on the tube, labelled at the bedside; request form signed. Compare the current group with previous records.
Topic 2
Major and minor cross-matching
Tests
Patient serum with donor red cells
Donor plasma with patient red cells
Importance
Essential — detects patient antibodies against donor cells
Less important now; donor plasma is screened and components contain little plasma
- 1Immediate spin (saline, room temperature) — detects ABO incompatibility (IgM)
- 2Incubation at 37 °C with albumin or LISS
- 3Antiglobulin phase — wash three times, add AHG reagent, centrifuge, read
- 4Validate negatives with Coombs control (IgG-coated) cells
- 5Compatible if no agglutination or haemolysis at any phase
- Type and screen: group plus antibody screen with reagent cells; electronic cross-match is allowed when screening is negative and systems are validated.
Topic 3
Enzymes in the blood bank
- Proteolytic enzymes (papain, bromelin, ficin) remove sialic acid and reduce the negative charge (zeta potential) of red cells, so IgG antibodies of Rh and Kidd systems agglutinate more strongly; they destroy some antigens (Duffy, MNS), so those antibodies are missed. Used in antibody identification and one-stage or two-stage techniques.
Topic 4
Coombs (antiglobulin) tests
Detects
Antibody or complement already on red cells in the body
Free antibody in serum that can coat red cells in vitro
Procedure
Wash patient cells; add AHG; centrifuge
Incubate serum with test cells at 37 °C; wash; add AHG
Uses
HDN, autoimmune haemolytic anaemia, transfusion reactions, drug-induced haemolysis
Cross-matching, antibody screening and identification, weak D, antenatal anti-D titre
Exam tip
Inadequate washing leaves free globulins that neutralise the AHG reagent — a false negative; always confirm negatives with Coombs control cells.
Topic 5
Hazards and complications of transfusion
Acute haemolytic (ABO incompatible)
Clerical error; IgM anti-A or anti-B; intravascular haemolysis
Fever, chills, back pain, hypotension, red urine, DIC, kidney failure — within minutes
Febrile non-haemolytic
Antibodies to donor leucocytes; cytokines
Fever and chills; prevented by leucoreduction
Allergic and anaphylactic
Plasma proteins; anti-IgA in IgA-deficient patients
Urticaria; anaphylaxis
Delayed haemolytic
Anamnestic IgG (Kidd, Rh) 3–14 days later
Falling Hb, jaundice, positive DAT
TRALI
Donor anti-HLA or anti-neutrophil antibodies
Acute lung injury within 6 hours
TACO
Volume overload
Breathlessness, hypertension
Infections
HIV, hepatitis B and C, malaria, syphilis, bacterial contamination (platelets)
Prevented by screening and good practice
Massive transfusion
Large volumes
Hypothermia, hyperkalaemia, hypocalcaemia (citrate), dilutional coagulopathy
Long-term
Repeated transfusion
Iron overload, alloimmunisation, TA-GvHD (prevented by irradiation)
Topic 6
Investigating a transfusion reaction
- 1
Stop transfusion; keep IV line open with saline; inform the doctor and blood bank
- 2
Check identities on bag, labels and patient (clerical check)
- 3
Return bag and giving set; collect post-transfusion blood (EDTA and clotted) and urine
- 4
Repeat ABO and Rh on pre- and post-transfusion samples and on the donor bag
- 5
Repeat cross-match; DAT on post-transfusion sample
- 6
Look for haemolysis: plasma Hb, bilirubin, LDH, haptoglobin, urine haemoglobin
- 7
Culture the bag if bacterial contamination is suspected
- 8
Document and report to haemovigilance (HvPI)
- Mismatched transfusion: most often due to identification errors at sample collection or bedside — prevented by two-person checks, barcoding and bedside verification.
Key terms
- Cross-match
- Compatibility test between donor and recipient
- AHG
- Antihuman globulin (Coombs) reagent
- DAT
- Test for antibodies coating red cells in vivo
- TRALI
- Transfusion-related acute lung injury
- Haemovigilance
- Surveillance of transfusion adverse events
Quick revision
- Sample within 3 days; identification.
- Major vs minor; immediate spin, 37 °C, AHG phases; Coombs control cells; type and screen.
- Enzymes enhance Rh and Kidd; destroy Duffy and MNS.
- DAT vs IAT uses.
- Reactions: AHTR, FNHTR, allergic, delayed, TRALI, TACO, infections, massive transfusion, iron overload, TA-GvHD; investigation steps; HvPI.
Important exam questions
Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).
Short-answer questions
- Q1.What does a major cross-match test?
- Q2.Why are Coombs control cells used?
- Q3.Which antigens are destroyed by papain?
- Q4.Give two uses of the direct Coombs test.
- Q5.What is the commonest cause of ABO-incompatible transfusion?
- Q6.How is TA-GvHD prevented?
Long-answer questions
- Q1.Describe cross-matching procedures.
- Q2.Describe the direct and indirect Coombs tests.
- Q3.Describe complications of blood transfusion.
- Q4.Describe the investigation of a transfusion reaction.
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