Q1ii / 15A14: Blood Types
15A14: Exam Report
How is blood typed and cross-matched?
38% of candidates passed this question.
An opening statement of the importance of compatibility testing helped explain the relevance of the process. A brief description/table of agglutinogens (membrane antigens) along with Agglutinins (IgM Antibodies) was helpful.
Typing is the testing of individual red blood cells (donor and recipient) with anti-sera containing anti-A, B and AB antibodies. A positive test results in agglutination. Red cells with known antigens (A, B and O) are then tested with sera (reverse grouping). When discussion antibody screening, a mention of Rhesus antibodies along with testing for minor antibodies (Kell, Duff etc.) was expected.
Cross matching consists of the saline agglutination test andiIndirect Coombs testing. (This involves incubation, washing and testing with antiglobulin serum).
Many answers confused the processes of typing, antibody screening and cross matching.
Q1ii / 15A14: How is blood typed & cross matched
- Blood transfusion = safe & compatible administration of blood products from donor to recipient
- Incompatibility = results in minor/major transfusion reactions & death
- Major antigens → responsible for TF reactions
ABO System
Group
O
Ag
None
Ab
Anti A & Anti B
Donor
Universal
Group
A
Ag
A
Ab
Anti B
Donor
Only to A
Group
B
Ag
B
Ab
Anti A
Donor
Only to B
Group
AB
Ag
A & B
Ab
None
Donor
Only to AB
Rhesus System
Group
Rh (+)
Rh (D) Ag
Present
Ab
Nil
Donor
To Rh (D) +
Group
Rh (-)
Rh (D) Ag
Absent
Ab
On exposure to Rh D (+) blood, develops anti-D
Donor
To Rh (D) + or –
3 Steps of Testing Blood Compatibility
1) Blood Grouping
- ABO & Rh(D) grouping
- Recipient red cells tested with anti-sera containing IgM Anti-A, Anti-B, Anti-AB Ab & Anti-D Abs
- Observe for agglutination
- +ve agglutination indicates blood type & Rhesus status
2) Antibody Screening
- >30 Ag’s on RBC
- Screen recipient serum for minor Ab which may cause agglutination e. Duffy
- Group matched RBC with minor Ag’s is added with patient serum → if there is +ve agglutination suggest problematic minor Abs → referred for Coombes Test
3) Cross Matching
- Mixes donor blood with recipient serum & observe for agglutination
- Immediate Spin XM
- Mixes donor red cells & recipient plasma
- Check for agglutination
- Only done if no clinically significant Ab detected in Ab screening
- Indirect Coombes’ Test
- Donor RBC & recipient serum is incubated
- Coombe’s reagent is added (Anti-Ig’s Abs)
- If donor RBC are coated with recipient serum Ab in incubation, adding Coombe’s reagent will cause agglutination
- Author: Krisoula Zahariou