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