Compatibility test

Dr. Topesh Patle

Introduction

  • Compatibility test in blood transfusion, also called crossmatching, is a pre-transfusion laboratory procedure.

  • It is performed to ensure that the donor’s blood is serologically compatible with the recipient’s blood.

  • The primary aim of compatibility testing is to prevent hemolytic transfusion reactions.

  • Hemolytic reactions occur when the recipient’s immune system attacks incompatible donor red blood cells (RBCs).

  • Compatibility testing includes ABO blood group compatibility, Rh factor compatibility, and crossmatching for other antibodies.

  • Even if ABO and Rh groups match, unexpected antibodies may still be present in the recipient’s serum.

  • Crossmatching helps in detecting these clinically significant antibodies before transfusion.

  • Compatibility testing is a mandatory and essential step in all blood transfusion services.

  • It plays a crucial role in ensuring patient safety and successful transfusion outcomes.

  • Proper compatibility testing is especially important for Blood Bank and MLT professionals involved in transfusion practices.

Purpose of Compatibility Testing

  • To ensure ABO blood group compatibility between donor and recipient.

  • To confirm Rh factor compatibility, especially to prevent Rh sensitization.

  • To detect unexpected or irregular antibodies present in the recipient’s serum.

  • To prevent acute hemolytic transfusion reactions caused by incompatible red blood cells.

  • To reduce the risk of delayed hemolytic transfusion reactions occurring days or weeks after transfusion.

  • To ensure safe selection of donor blood for transfusion.

  • To act as a final serological check before issuing blood for transfusion.

  • To minimize transfusion-related morbidity and mortality.

  • To prevent clerical and technical errors in blood transfusion practice.

  • To ensure patient safety and successful transfusion therapy.

Types of Compatibility Tests for Blood Transfusion

Compatibility testing in blood transfusion consists of a series of laboratory tests performed systematically to ensure safe transfusion. The major types of compatibility tests are as follows:

  1. ABO Compatibility Test
  2. Rh Compatibility Test
  3. Crossmatching Test

 

ABO Compatibility Test

The ABO compatibility test is the first and most critical step in compatibility testing for blood transfusion. It ensures that the ABO blood group of the donor and recipient are serologically compatible before transfusion.

  • The ABO blood group system is based on the presence or absence of A and B antigens on the surface of red blood cells and the corresponding naturally occurring antibodies (anti-A and anti-B) in plasma.

  • ABO incompatibility can result in severe, immediate, and potentially fatal hemolytic transfusion reactions.

  • These reactions occur because the recipient’s pre-formed antibodies rapidly bind to incompatible donor red blood cells, causing agglutination and intravascular hemolysis.

  • Therefore, correct ABO grouping of both donor and recipient is mandatory before any blood transfusion.

Principle

  • Donor red blood cells must not contain A or B antigens against which the recipient has circulating antibodies.

  • Any mismatch between donor antigens and recipient antibodies leads to agglutination or hemolysis, indicating incompatibility.

ABO Compatibility Pattern

Donor Blood Group Compatible Recipient Blood Group
O O, A, B, AB
A A, AB
B B, AB
AB AB only

 

Special Considerations

    • Group O red cells, particularly O negative, are preferred in emergency transfusions due to absence of A, B, and Rh (D) antigens.

    • Group AB individuals can receive red cells from all ABO groups, as they lack anti-A and anti-B antibodies.

 

Rh Compatibility Test

The Rh compatibility test is an essential part of pre-transfusion testing performed after ABO compatibility has been established. It ensures that the Rh (D) antigen status of the donor and recipient are compatible, thereby preventing immune sensitization and transfusion reactions.

  • The Rh blood group system is primarily concerned with the D antigen, which is highly immunogenic.

  • Individuals who possess the D antigen are classified as Rh positive, while those lacking it are Rh negative.

  • Unlike the ABO system, Rh antibodies are not naturally occurring; they are formed only after exposure to Rh-positive red blood cells through transfusion or pregnancy.

Principle

  • Rh incompatibility occurs when a Rh-negative recipient receives Rh-positive blood.

  • This exposure may stimulate the formation of anti-D antibodies in the recipient.

  • Subsequent transfusions with Rh-positive blood can result in hemolytic transfusion reactions, which may be severe.

Compatibility Rules

  • Rh-negative individuals should receive only Rh-negative blood.

  • Rh-positive individuals can safely receive Rh-positive or Rh-negative blood.

Rh Compatibility Pattern

Donor Rh Type Recipient Rh Type Compatibility
Rh+ Rh+ Compatible
Rh− Rh+ or Rh− Compatible
Rh+ Rh− Incompatible

 

Clinical Significance

    • Rh compatibility testing is especially important in:

      • Patients requiring multiple transfusions

      • Women of child-bearing age, to prevent Rh alloimmunization

    • Proper Rh matching reduces the risk of future transfusion reactions and immune complications.

 

Crossmatching Test

The crossmatching test is a final and confirmatory step in compatibility testing, performed after ABO and Rh compatibility have been established. Its primary purpose is to ensure that no clinically significant antibodies present in the recipient’s serum will react with the donor’s red blood cells during transfusion.

  • Even when ABO and Rh groups are compatible, unexpected (irregular) antibodies may be present in the recipient’s blood.

  • These antibodies can cause agglutination or hemolysis of donor red blood cells, leading to transfusion reactions.

  • Crossmatching therefore acts as a safety check before the release of blood for transfusion.

Types of Crossmatching

A. Major Crossmatch

The major crossmatch is the most critical and mandatory component of compatibility testing in blood transfusion. It is performed to determine whether the recipient’s serum contains antibodies that can react with the donor’s red blood cells (RBCs).

Failure to detect incompatibility at this stage can result in severe or fatal hemolytic transfusion reactions.

 

 

Principle

  • Recipient serum may contain IgG or IgM antibodies formed due to:
    • Previous transfusions
    • Pregnancy
    • Exposure to foreign red cell antigens
  • If donor RBCs possess antigens corresponding to these antibodies:
    • Antigen–antibody reaction occurs
    • Leads to agglutination or hemolysis
  • Absence of such reaction indicates compatibility

Specimen Required

  • Recipient: Serum or plasma
  • Donor: Red blood cells (prepared as a 2–5% cell suspension in saline)

Major Crossmatch Procedure (Tube Method – Stepwise)

 Sample Preparation

  • Properly labeled blood samples are collected from both donor and recipient
  • Donor RBCs are washed and prepared as a suspension
  • Recipient serum/plasma is separated

 Mixing

  • Recipient serum/plasma is mixed with donor red cell suspension in a test tube

Testing Phases

 Phase I: Immediate Spin (IS Phase)

  • Centrifugation at room temperature
  • Detects ABO incompatibility
  • Agglutination at this stage indicates immediate incompatibility

Phase II: Incubation at 37°C

  • Tube incubated at 37°C for 30–60 minutes
  • Enhances detection of incomplete (IgG) antibodies
  • Weak antigen–antibody reactions may appear

Phase III: Antiglobulin (AHG) Phase

  • Anti-human globulin reagent is added
  • Detects RBCs sensitized with IgG antibodies
  • Most sensitive and confirmatory phase

 Interpretation of Results

Observation Interpretation Action
No agglutination / no hemolysis Compatible Blood can be issued
Agglutination present Incompatible Blood must not be transfused
Hemolysis present Incompatible High risk – reject unit

 

 Causes of Incompatible Major Crossmatch

  • ABO grouping error
  • Presence of unexpected alloantibodies (e.g., Kell, Duffy, Kidd)
  • Autoimmune hemolytic anemia
  • Recent transfusion or pregnancy
  • Technical or clerical errors

 Clinical Significance

  • Major crossmatch primarily protects the recipient
  • Prevents:
    • Acute hemolytic transfusion reactions
    • Shock and renal failure
    • Transfusion-related mortality
  • Considered more important than minor crossmatch

 

B. Minor Crossmatch

The minor crossmatch is a component of compatibility testing in which the donor’s serum or plasma is tested against the recipient’s red blood cells.
Its purpose is to detect antibodies present in the donor’s plasma that may react with antigens on the recipient’s red blood cells.

Principle

  • Donor plasma may contain antibodies formed due to previous transfusions or pregnancy.

  • If recipient RBCs carry corresponding antigens:

    • Antigen–antibody reaction may occur

    • Results in agglutination or hemolysis

  • Absence of reaction indicates compatibility.

 Specimen Required

  • Donor: Serum or plasma

  • Recipient: Red blood cells (2–5% cell suspension)

 Minor Crossmatch Procedure (Tube Method)

  1. Sample Collection

    • Properly labeled blood samples are collected from donor and recipient.

  2. Preparation

    • Recipient red blood cells are washed and prepared as a suspension.

    • Donor serum or plasma is separated.

  3. Mixing

    • Donor serum/plasma is mixed with recipient RBC suspension.

  4. Incubation and Testing

    • Tested through immediate spin and, if required, incubation and AHG phases.

  5. Observation

    • The mixture is examined for agglutination or hemolysis.

 Interpretation of Results

Observation Interpretation
No agglutination / no hemolysis Compatible
Agglutination present Incompatible
Hemolysis present Incompatible

 

 Clinical Significance

  • Minor crossmatch detects antibodies that could:

    • Cause mild to moderate transfusion reactions

    • Lead to hemolysis if large volumes of donor plasma are transfused

  • Historically important when whole blood transfusions were common.

 

MCQs

1. Compatibility testing in blood transfusion is also known as

A. Blood grouping
B. Antibody screening
C. Crossmatching
D. Typing

✔ Answer: C

2. The main purpose of compatibility testing is to prevent

A. Infection
B. Allergic reaction
C. Hemolytic transfusion reaction
D. Febrile reaction

✔ Answer: C

3. Which test is performed first in compatibility testing?

A. Crossmatch
B. Rh typing
C. Antibody screening
D. ABO compatibility test

✔ Answer: D

4. ABO incompatibility can cause

A. Delayed hemolysis
B. Immediate severe hemolysis
C. Mild allergic reaction
D. No reaction

✔ Answer: B

5. Naturally occurring antibodies are seen in

A. Rh system
B. Kell system
C. ABO system
D. Duffy system

✔ Answer: C

6. Universal donor for red cell transfusion is

A. AB+
B. O+
C. O−
D. AB−

✔ Answer: C

7. Universal recipient for red cell transfusion is

A. O−
B. A+
C. B+
D. AB+

✔ Answer: D

8. Rh antibodies are

A. Naturally present
B. Always IgM
C. Immune antibodies
D. Cold antibodies

✔ Answer: C

9. Rh-negative individuals should receive

A. Rh-positive blood
B. Rh-negative blood only
C. Any blood group
D. Whole blood only

✔ Answer: B

10. Which antigen is most important in Rh system?

A. C
B. c
C. E
D. D

✔ Answer: D

11. Crossmatching is performed after

A. Antibody identification
B. ABO and Rh testing
C. Donor screening
D. Blood storage

✔ Answer: B

12. Major crossmatch involves

A. Donor serum + Recipient RBCs
B. Recipient serum + Donor RBCs
C. Donor plasma + Donor RBCs
D. Recipient plasma + Recipient plasma

✔ Answer: B

13. Major crossmatch detects

A. Donor antibodies
B. Recipient antibodies
C. Autoantibodies only
D. Platelet antibodies

✔ Answer: B

14. The most important crossmatch is

A. Minor crossmatch
B. Auto-control
C. Major crossmatch
D. Electronic crossmatch

✔ Answer: C

15. Minor crossmatch involves

A. Recipient serum + Donor RBCs
B. Donor serum + Recipient RBCs
C. Recipient serum + Recipient RBCs
D. Donor serum + Donor RBCs

✔ Answer: B

16. Minor crossmatch is rarely done because

A. It is expensive
B. It is unreliable
C. Donor plasma is minimal in PRBCs
D. It takes long time

✔ Answer: C

17. Agglutination during crossmatch indicates

A. Compatibility
B. Normal reaction
C. Incompatibility
D. Weak positive

✔ Answer: C

18. Hemolysis during crossmatch indicates

A. Safe transfusion
B. Incompatibility
C. Antibody absence
D. Technical error only

✔ Answer: B

19. Immediate spin crossmatch mainly detects

A. Rh incompatibility
B. ABO incompatibility
C. IgG antibodies
D. Autoantibodies

✔ Answer: B

20. Antiglobulin (AHG) phase detects

A. IgM antibodies
B. Complement only
C. IgG antibodies
D. Cold antibodies

✔ Answer: C

21. Antibody screening is done to detect

A. ABO antibodies
B. Unexpected antibodies
C. Rh antibodies only
D. Autoantibodies only

✔ Answer: B

22. Kell, Kidd, and Duffy antibodies are

A. Naturally occurring
B. Clinically insignificant
C. Unexpected antibodies
D. Cold antibodies

✔ Answer: C

23. Crossmatch compatible means

A. Blood can be issued
B. Blood must be rejected
C. Repeat testing needed
D. Antibody present

✔ Answer: A

24. Crossmatch incompatible means

A. Safe transfusion
B. Delay transfusion
C. Do not issue blood
D. Emergency transfusion

✔ Answer: C

25. Which component requires crossmatching?

A. Platelets
B. Plasma
C. Red cell concentrates
D. Cryoprecipitate

✔ Answer: C

26. Major crossmatch primarily protects

A. Donor
B. Blood bank
C. Recipient
D. Technician

✔ Answer: C

27. Delayed hemolytic transfusion reaction occurs due to

A. ABO mismatch
B. Rh mismatch
C. Weak or undetected antibodies
D. Bacterial contamination

✔ Answer: C

28. Which test is mandatory before issuing blood?

A. Minor crossmatch
B. Major crossmatch
C. Auto-control
D. Coombs test

✔ Answer: B

29. Auto-control detects

A. Donor antibodies
B. Recipient autoantibodies
C. ABO incompatibility
D. Rh incompatibility

✔ Answer: B

30. Crossmatching is a

A. Screening test
B. Confirmatory test
C. Diagnostic test
D. Prognostic test

✔ Answer: B

31. Incorrect labeling may cause

A. Storage error
B. Clerical error
C. Reagent failure
D. Equipment failure

✔ Answer: B

32. Which blood is preferred in emergencies?

A. AB+
B. A−
C. O−
D. B+

✔ Answer: C

33. ABO antibodies are usually

A. IgG
B. IgM
C. IgE
D. IgA

✔ Answer: B

34. Rh antibodies are usually

A. IgM
B. IgE
C. IgG
D. IgA

✔ Answer: C

35. Which reaction is most dangerous?

A. Allergic reaction
B. Febrile reaction
C. Acute hemolytic reaction
D. Mild hemolysis

✔ Answer: C

36. Crossmatch must be repeated if

A. Blood stored properly
B. Patient transfused recently
C. Donor healthy
D. Blood is fresh

✔ Answer: B

37. Whole blood transfusion increases risk of

A. Minor incompatibility
B. ABO mismatch
C. Rh mismatch
D. Infection

✔ Answer: A

38. Which method is gold standard for teaching?

A. Gel method
B. Tube method
C. Solid phase method
D. Automation

✔ Answer: B

39. Absence of agglutination indicates

A. Error
B. Incompatibility
C. Compatibility
D. Weak reaction

✔ Answer: C

40. Crossmatch should be documented to prevent

A. Hemolysis
B. Infection
C. Transfusion errors
D. Antibody formation

✔ Answer: C

41. Recipient antibodies are formed due to

A. Diet
B. Infection
C. Transfusion or pregnancy
D. Age

✔ Answer: C

42. Crossmatching is done mainly for

A. Plasma transfusion
B. Platelet transfusion
C. Red cell transfusion
D. Cryoprecipitate

✔ Answer: C

43. Which phase is most sensitive?

A. Immediate spin
B. Incubation
C. AHG phase
D. Room temperature

✔ Answer: C

44. A hemolytic reaction can cause

A. Fever only
B. Kidney failure
C. Mild rash
D. Headache only

✔ Answer: B

45. Crossmatch incompatibility requires

A. Emergency transfusion
B. Issue same unit
C. Selection of another donor unit
D. Ignore result

✔ Answer: C

46. Compatibility testing ensures

A. Donor safety
B. Technician safety
C. Patient safety
D. Equipment safety

✔ Answer: C

47. Antibody screening is done using

A. Donor RBCs
B. Screening cells
C. Recipient RBCs
D. Saline only

✔ Answer: B

48. Which antibody is clinically significant?

A. Anti-A
B. Anti-B
C. Anti-Kell
D. Anti-H

✔ Answer: C

49. Crossmatching is the _____ step before transfusion

A. First
B. Optional
C. Final
D. Preliminary

✔ Answer: C

50. Compatibility testing is mandatory in

A. Research labs
B. Diagnostic labs
C. Blood banks
D. Pathology labs

✔ Answer: C