Unit 1: Blood group systems and grouping technique
Blood Banking notes · PTU syllabus (BMLS603-18)
On this page
- Unit summary
- History of blood groups
- The ABO system
- The Rh system
- Blood grouping methods and errors
- Complete and incomplete antibodies
- Secretor status: A and B substances
- Titration and storage of grouping antisera
- Anticoagulants used in transfusion
- Donor selection and blood collection
- Key terms
- Quick revision
- Important questions
Unit summary
Safe transfusion starts with correct blood grouping. This unit covers the history of blood groups, the ABO and Rh systems, errors in grouping, complete and incomplete antibodies, secretor status, titration and storage of antisera, anticoagulants for transfusion and donor blood collection.
After this unit you can
- Describe the ABO and Rh blood group systems
- Perform forward and reverse grouping and avoid errors
- Explain complete and incomplete antibodies and secretor status
- Select and screen donors and collect blood correctly
PTU syllabus topics
- Introduction to and history of blood group systems
- ABO and Rh blood group systems
- sources of error in blood grouping
- complete vs incomplete antibodies
- tests for A/B substance secretion
- titration and storage of grouping antisera
- anticoagulants used in transfusion
- procedure for donor blood collection
Group A
A
Anti-B
Group B
B
Anti-A
Group AB
A and B
None: universal plasma recipient
Group O
None
Anti-A and anti-B: universal red cell donor
Topic 1
History of blood groups
- 1
Landsteiner (1900–1901)
Discovers A, B and O groups — Nobel Prize 1930
- 2
Decastello and Sturli (1902)
Group AB
- 3
Lewisohn and Hustin (1914–1915)
Citrate anticoagulant
- 4
Landsteiner and Wiener (1940)
Rh factor
- 5
Coombs, Mourant and Race (1945)
Antiglobulin test
- 6
1990s onward
Component therapy, NAT testing of donors
Topic 2
The ABO system
A
A
Anti-B
B
B
Anti-A
AB
A and B
None — universal recipient of red cells
O
None (H antigen)
Anti-A and anti-B — universal donor of red cells
- ABO antibodies are naturally occurring IgM (complete) antibodies appearing at 3–6 months. Subgroups: A1 and A2 (A2 about 20% of A); Bombay phenotype (Oh) lacks H antigen and has anti-H — first described in Mumbai; compatible only with Bombay blood.
- Frequency in India (approximate): B about 32–37%, O about 29–37%, A about 22–24%, AB about 6–8%.
Topic 3
The Rh system
- Main antigen D; Rh-positive (D present) in about 93–95% of Indians. Other antigens C, c, E, e. Anti-D is not naturally present — formed after exposure by transfusion or pregnancy (IgG, incomplete).
- Weak D (Du): reduced D expression detected by the antiglobulin phase — treat as Rh-positive as a donor and Rh-negative as a recipient.
- Haemolytic disease of the newborn: an Rh-negative mother sensitised by an Rh-positive fetus makes anti-D that crosses the placenta in later pregnancies; prevented by anti-D immunoglobulin at 28 weeks and within 72 hours after delivery.
Topic 4
Blood grouping methods and errors
Tests
Patient red cells with anti-A, anti-B, anti-D (and anti-AB)
Patient serum with known A, B and O cells
Detects
Antigens
Antibodies
Purpose
Determine group
Confirm the cell group; must agree
- Slide method
- Quick; less sensitive — screening only
- Tube method
- Standard; centrifugation enhances reactions
- Microplate
- Batch testing
- Column agglutination (gel cards)
- Standardised, objective reading
- Clerical
- Wrong labelling or recording — the commonest cause of ABO-incompatible transfusion
- Technical
- Wrong cell suspension strength (use 2–5%), contaminated or expired antisera, inadequate centrifugation, failing to read promptly
- Patient-related
- Weak subgroups, newborns (no antibodies), elderly (weak antibodies), rouleaux, cold agglutinins, recent transfusion or bone marrow transplant
Exam tip
Forward and reverse grouping must match; any discrepancy must be resolved before blood is issued.
Topic 5
Complete and incomplete antibodies
Class
Mostly IgM
Mostly IgG
Agglutination in saline
Yes
No — sensitise cells only
Detection
Immediate spin in saline at room temperature
Antiglobulin (Coombs) test, enzyme or albumin methods at 37 °C
Examples
Anti-A, anti-B
Anti-D, Kell, Duffy, Kidd antibodies
Placenta
Do not cross
Cross — cause HDN
Topic 6
Secretor status: A and B substances
- About 80% of people are secretors (Se gene): water-soluble A, B and H substances in saliva and other secretions.
- 1Collect saliva; boil to destroy enzymes; centrifuge
- 2Mix supernatant with diluted anti-A, anti-B and anti-H (lectin from Ulex europaeus)
- 3Incubate
- 4Add the corresponding A, B or O indicator cells
- 5No agglutination = substance present (antibody neutralised) — secretor
Topic 7
Titration and storage of grouping antisera
- Titration: doubling dilutions of antiserum tested with corresponding cells; titre = reciprocal of the highest dilution giving agglutination (good anti-A and anti-B titre 1:256 or more; avidity — agglutination within 10–15 seconds on a slide).
- Storage: 2–8 °C, protect from light and contamination; do not freeze-thaw repeatedly; check daily with known positive and negative cells; discard after expiry.
Topic 8
Anticoagulants used in transfusion
ACD
Acid citrate dextrose
21 days
CPD
Citrate, phosphate, dextrose
21 days
CPDA-1
CPD with adenine
35 days
SAGM (additive)
Saline, adenine, glucose, mannitol added to red cells
42 days for packed red cells
- Roles: citrate binds calcium (anticoagulant); dextrose fuels red cells; phosphate buffers pH; adenine maintains ATP. Store red cells at 2–6 °C.
Topic 9
Donor selection and blood collection
- Age
- 18–65 years (first-time donors up to 60)
- Weight
- 45 kg or more (for 350 mL), 55 kg for 450 mL
- Haemoglobin
- 12.5 g/dL or more
- Interval
- At least 90 days for men and 120 days for women between whole blood donations
- Health
- Normal pulse, BP and temperature; no high-risk behaviour; deferral after tattoos (12 months), recent illness, pregnancy
- 1
Registration, questionnaire and informed consent
- 2
Medical examination and Hb check
- 3
Clean the arm with antiseptic (povidone-iodine then alcohol)
- 4
Venepuncture of the antecubital vein with a sterile closed bag system
- 5
Collect 350 or 450 mL with continuous mixing; divert first 20–30 mL into a pouch for tests
- 6
Seal tubing; label bag and samples with the same number
- 7
Rest and refreshments; observe for reactions
- Mandatory screening of every unit: HIV 1 and 2, hepatitis B (HBsAg), hepatitis C, syphilis and malaria; ABO and Rh grouping; antibody screening (recommended); NAT where available.
Key terms
- Agglutination
- Clumping of red cells by antibodies
- Reverse grouping
- Testing serum against known red cells
- Bombay phenotype
- Rare phenotype lacking H antigen
- Secretor
- Person with ABH substances in secretions
- CPDA-1
- Anticoagulant-preservative allowing 35 days' storage
Quick revision
- Landsteiner; ABO antigens and antibodies; subgroups; Bombay; Indian frequencies.
- Rh D; weak D; HDN and anti-D prophylaxis.
- Forward and reverse grouping; methods; errors.
- IgM complete vs IgG incomplete; Coombs.
- Secretor test; antiserum titre and storage; ACD, CPD, CPDA-1, SAGM; donor criteria; collection; mandatory screening.
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.Who discovered the ABO system?
- Q2.Which group is the universal red cell donor?
- Q3.What is the Bombay phenotype?
- Q4.Why is reverse grouping done?
- Q5.Distinguish complete and incomplete antibodies.
- Q6.How long can blood in CPDA-1 be stored?
Long-answer questions
- Q1.Describe the ABO and Rh blood group systems.
- Q2.Describe blood grouping techniques and sources of error.
- Q3.Describe donor selection and blood collection.
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