Life's Blood

THE CROSSMATCH

General Information

The Crossmatch also known as compatibility testing,  pretransfusion testing or type and crossmatch (Type and Cross; T & C).  The definition of a compatibility test (crossmatch) is a series of procedures use to give an indication of blood group compatibility between the donor and the recipient and to detect irregular antibodies in the recipient's serum.

The main purpose for performing a crossmatch is to promote (not ensure) the safe transfusion of blood. We are performing testing to the best of our ability that will demonstrate that the donor blood is compatible with the recipient's blood.  Crossmatch procedures should be designed for speed and accuracy - get the safest blood reasonably possible available to the patient as soon as possible.  In summary, the AABB Technical Manual  states the goals of a compatibility test is to:

• Detect as many clinically significant antibodies as possible
• Detect as few clinically insignificant antibodies as possible
• Complete the procedure in a timely manner. (p. 379)

Once donor blood is crossmatched with a potential recipient, the results of the crossmatch is good only 3 days. If the physician wants the donor blood available longer, we must get a new recipient sample and repeat tests.  This protocol helps detect new antibodies that may be forming, especially when patient has been transfused within past three months.

Parts of the Crossmatch

The AABB Standards for Blood Banks and Transfusion Services requires that certain procedures are performed before blood is transfused to a recipient:

• Identification of the recipient and recipient blood sample is crucial since the major of the hemolytic transfusion reactions are due to errors in patient or sample identification.
• ABO and Rh typing of the recipient's blood and resolving any ABO discrepancies.  If the discrepancy can not be resolved before the patient needs the transfusion type O blood should be given. If problems arise with the D testing, Rh negative blood should be given.
• Performing an antibody screen on the recipient's serum for clinically significant antibodies.  These antibodies are most likely to occur in the 37^oC and AGT phases of testing.  Each negative AGT test must be followed by "Coombs Control Check Cells." An autocontrol may or may not be used.  Some labs prefer to perform this routinely during the antibody screen while others will only include it if an antibody needs to be identified.  The autocontrol has to be part of the antibody identification procedure.  The SOP of each institution must be followed by all individuals performing these tests.
• Comparing present findings with previous records for the recipient.  If previous testing has been performed on the recipient and should match current testing. These comparisons can give assurance that no identification errors have occurred, but it is not proof.  Records would also show if clinically significant antibodies have been detected in the past.  These antibodies may be presently at undetectable levels.  Any history of clinically significant antibodies, even if  undetectable now in the patient, dictates an antiglobulin phase crossmatch needs to be done between the recipient's serum and the donor's cells.
• Confirmation of the ABO and Rh type of the red cell components being given when the shipment of blood is received in the laboratory.
• Selection of appropriate ABO and Rh component units for the recipient first would be the same ABO and Rh type.  Transfused donor red cells must be ABO compatible with the patient's plasma and whatever antibodies may be present.  Transfused plasma must be ABO compatible with the recipient's red cells. 

  AABB Technical Manual's Table 18-2 Selection of Components When ABO-Identical Donors Are Not Available, p 385
  	ABO Requirements
  Whole Blood	Must be identical to that of the recipient
  Red Blood Cells (most plasma removed)	Must be compatible with the recipient's plasma.
  Granulocytes, Pheresis	Must be compatible with the recipient's plasma.
  Fresh Frozen Plasma	Must be compatible with the patient's red cells.
  Platelets, Pheresis	All blood groups acceptable; components compatible with the recipient's red cells preferred
  Cryoprecipitated AHF	All ABO groups acceptable

   Rh-positive components should be given to  Rh-positive individuals and Rh-negative units should be reserved for D-negative individuals.  The physician needs to be involved in any decisions relating to giving Rh-positive blood to an Rh-negative individuals since those individuals have an 80% chance of making an anti-D following transfusion.

• Perform a crossmatch either serologically or via a computer. If no clinically significant antibodies are found in the recipient the institution has the option of choosing an immediate-spin crossmatch (serologic technique) or a computer crossmatch.  If clinically significant antibodies are found, an antiglobulin crossmatch must be performed.
• Label the components with the recipient's identifying information

Type and Screen

The type and screen consists of ABO/Rh, antibody screen, and a  records check.  This order is used when likelihood of needing blood is low.  Therefore, no donor blood crossmatched to patient.  If need for blood suddenly arises, you can take sample that is already typed and screened, and perform a crossmatch with donor units from the specimen.  Type and screen protocol  cannot be used if patient has an antibody.  Then an antiglobulin crossmatch must be performed.

Benefits of a Crossmatch

Performing a crossmatch before transfusing blood has the following benefits:

• Detects major ABO errors (ie. crossmatching an A donor with an O or B recipient )
   
• Detects most recipient antibodies to antigens on donor red cells (if the antibody is in high enough titer to react)  One of the most common clinically significant antibodies that are missed are the Kidd antibodies.

Limitations of a Crossmatch:

A crossmatch also has limitations:

• Will not detect errors in patient identification (unless a previous record exists)
• Will not detect ABO mix-ups if blood types are compatible (can crossmatch group A donor blood for an AB recipient)
• Will not detect Rh errors (can crossmatch Rh+ donor blood with Rh negative recipient with no reaction if the patient has no anti-D)
• Will not detect all recipient antibodies to donor antigens (antibody may be too weak to detect, but still cause transfusion reaction such as the Kidd antibodies)
• Will not prevent alloimmunization of recipient (only ABO and Rh antigens matched - patient can potentially make antibody to all the other antigens)  This is why many of the discovered antibodies are found in multi-transfused patients.

Immediate Spin versus Antiglobulin, Coombs, Crossmatch

The purpose of Immediate spin step of crossmatch is to detect major ABO incompatibility between donor and recipient.  ABO incompatibility is the most common life-threatening type of transfusion reaction and is often due to clerical errors.

It is permissible to stop at immediate spin step of crossmatch if:

1. Immediate spin is negative and
2. Antibody screen is negative in all phases and
3. There is no record of previous antibodies

It is NOT permissible to stop at the immediate spin step and you must incubate and carry crossmatch through antiglobulin, Coombs, phase if:

• Immediate Spin test agglutinated or
• Patient has an antibody (screening cells are positive) or
• Patient has a record of a previous antibody

Benefits of an Immediate Spin only crossmatch:

• Makes blood available to patient faster
• More cost-effective
• 90% of patients are eligible for immediate-spin crossmatches

Electronic or Computer Crossmatch As An Alternative to the immediate-spin crossmatch

An institution may choose to perform computer crossmatches instead of an immediate-spin crossmatch. They must meet specific criteria in order to do electronic crossmatches.  Electronic crossmatches have no mixing of patient serum and donor cells in test tube - computer verifies ABO/Rh compatibility of donor and recipient

1. Computer system must be FDA-approved and validated to do this
2. Patient ABO/Rh must have been typed at least twice - by two different technologists
3. Patient has no antibodies and no record of previous antibodies
4. Donor information must be bar-coded into computer inventory for accuracy
5. Computer does not allow use of donor unit until its ABO/Rh is verified
6. Computer does not allow issue of ABO/Rh incompatible blood

Crossmatch Problems:

OBJECTIVES - COMPATIBILITY TESTING

1. Discuss the steps in compatibility testing and explain their purpose.
2. Discuss the reasons for compatibility testing.
3. Discuss the limitations of compatibility testing.
4. Explain what a Type and Screen consists of, and when it would be used.
5. Explain when a LISS-Coombs crossmatch would be done versus an immediate-spin crossmatch.
6. Explain what an electronic crossmatch is.
7. Describe what additional testing must be done when crossmatching a patient with an antibody.
8. Describe how to determine the number of units to screen when crossmatching blood for a patient with an antibody
9. Discuss how to resolve the following problems encountered in compatibility testing:

• Test results not matching previous records
• Screening cells positive at room temperature, negative in Coombs
• Screening cells positive in Coombs only - new antibody
• Screening cells positive in Coombs only - previously identified antibody
• Screening cells positive both at RT and in Coombs
• Negative screening cells, but records show a previously-identified antibody
• Negative screening cells but crossmatch positive at immediate spin
• Positve autocontrol

10. State how long you may keep blood crossmatched, before having to get a new sample and repeat the test

Performance objectives:

1. Correctly perform, interpret and report a compatibility test on any given sample
2. Correctly identify, document and resolve any problems associated with compatibility testing.