Cross-matching
Cross-matching blood, in transfusion medicine, refers to the complex testing that is performed prior to a blood transfusion, to determine if the donor's blood is compatible with the blood of an intended recipient, or to identify matches for organ transplants. Cross-matching is usually performed only after other, less complex tests have not excluded compatibility. Blood compatibility has many aspects, and is determined not only by the blood types (O,A,B,AB), but also by blood factors, (Rh, Kell, etc.)
Cross-matching is done by a certified laboratory technologist, in a laboratory. It can be done electronically, with a computer database, or serologically. Simpler tests may be used to determine blood type (only), or to screen for antibodies (only). (indirect Coombs test).
Contents- 1 Types of cross-matching
- 1.1 Electronic cross-matching
- 1.2 Serological cross-matching
Types of cross-matching Electronic cross-matching
Electronic cross-matching is essentially a computer-assisted analysis of the data entered from testing done on the donor unit and blood samples drawn from intended recipient. This includes ABO/Rh typing of the unit and of the recipient, and an antibody screen of the recipient. Electronic cross-matching can only be used if a patient has a negative antibody screen, which means that they do not have any active red blood cell atypical antibodies, or they are below the detectable level of current testing methods. If all of the data entered is compatible, the computer will print a compatibility label stating that the unit is safe to transfuse.
Serological cross-matching
In serological cross-matching, red blood cells from the donor unit are tested against the plasma of the patient in need of the blood transfusion. If the patient’s serum contains antibodies against the antigens present on the donor red blood cells, agglutination will occur. Agglutination is considered a positive reaction indicating that the donor unit is incompatible for that specific patient. If no agglutination occurs the unit is deemed compatible and is safe to transfuse.
Emergencies
In the case of an emergency a physician can request "uncross-matched blood", or donor units of blood that have not been cross-matched. It is thought that this lifesaving measure is of more benefit than any risk of an antibody-mediated transfusion reaction. In addition, the risk of a serious transfusion reaction can be minimized if the donor unit is both ABO-compatible and Rhesus (Rh)-compatible. Type O and Rh negative blood can be given if the recipient's blood group is not known, as may happen in an emergency. In an emergency, blood grouping can be done easily and quickly in 2 or 3 minutes in the laboratory on glass slides with appropriate reagents, by trained technical staff. This method depends on the presence or absence of agglutination, which can usually be visualized directly, although occasionally a light microscope may be needed. If laboratory services are not available, another system of deciding which type of blood to use in an emergency is the bedside card method of blood grouping, where a drop of the intended recipients' blood is added to dried reagents on a prepared card. This method may not be as reliable as laboratory methods, which are preferable.
- Disclaimers
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 37oC 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 BloodMust be identical to that of the recipient
Red Blood Cells (most plasma removed)Must be compatible with the recipient's plasma.
Granulocytes, PheresisMust be compatible with the recipient's plasma.
Fresh Frozen PlasmaMust be compatible with the patient's red cells.
Platelets, PheresisAll blood groups acceptable; components compatible with the recipient's red cells preferred
Cryoprecipitated AHFAll 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:
Immediate spin is negative and
Antibody screen is negative in all phases and
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
Computer system must be FDA-approved and validated to do this
Patient ABO/Rh must have been typed at least twice - by two different technologists
Patient has no antibodies and no record of previous antibodies
Donor information must be bar-coded into computer inventory for accuracy
Computer does not allow use of donor unit until its ABO/Rh is verified
Computer does not allow issue of ABO/Rh incompatible blood
Crossmatch Problems:
OBJECTIVES - COMPATIBILITY TESTING
Discuss the steps in compatibility testing and explain their purpose.
Discuss the reasons for compatibility testing.
Discuss the limitations of compatibility testing.
Explain what a Type and Screen consists of, and when it would be used.
Explain when a LISS-Coombs crossmatch would be done versus an immediate-spin crossmatch.
Explain what an electronic crossmatch is.
Describe what additional testing must be done when crossmatching a patient with an antibody.
Describe how to determine the number of units to screen when crossmatching blood for a patient with an antibody
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
State how long you may keep blood crossmatched, before having to get a new sample and repeat the test
Chart Of A-B-O Blood Donor & Recipient Compatibility
RECIPIENT
D
O
N
O
RAlleles &
Antibodies O
anti-A
anti-B A
anti-B B
anti-A AB
None
ONoneNoneNoneNone
AClumpNoneClumpNone
BClumpClumpNoneNone
ABClumpClumpClumpNone
Chart of A-B-O Blood Donor-Recipient Compatibility. Serious problems may arise when the antibodies of the recipient clump the blood cells of the donor. [The reverse scenario is not as serious because the antibodies of the donor are diluted by the recipient's blood volume.] Clumping of the donor's blood is indicated by the word "Clump" in the red squares. No clumping of the donor's blood is indicated by the word "None" in the green squares. None also denotes the lack of anti-A or anti-B antibodies in the type O recipient. It is clear from this chart that the "universal donor" is type O, while the "universal recipient" is type AB. If you include the Rh factor, then the universal donor becomes O Negative while the universal recipient becomes AB Positive.
Simplified Explanation For Rh Blood Factor
Rh Neg
Blood
Add a drop of anti-Rh antibodies (anti-D serum) to a drop of blood
on a slide labeled Rh. The Rh negative blood (shown above) will
not clump, while the Rh positive blood (below) will show clumping:
Rh Pos
Blood
Placing the Rh slide on a warming box will hasten the agglutination reaction. Backlighting will also make it easier to see the clusters of agglutinated red blood cells that appear like minute grains of sand in the blood. Rocking the slide back and forth also makes it easier to see the grainy texture of the agglutinated blood.
An Rh Blood Typing (Warming) Box.
Remember that the anti-Rh serum will only agglutinate the positive D factor. There are technically three positive genes called C, D and E. The negative alleles for these three genes are usually denoted by small case c, d and e. This is an example of multiple gene (polygenic) inheritance which is explained in more detail at the following URL:
Multiple Gene Inheritance In The Rh Factor
Although it is much more complicated, the Rh blood factor can be explained by a pair of alleles on homologous chromosome pair #1. The dominant Rh positive gene (+) produces the Rh antigen, a glycoprotein constituent of the RBC membrane (see above Rh positive RBC illustration). Like the type O gene, the recessive Rh negative gene (-) does not produce an antigen. The following table summarizes Rh inheritance in humans:
Blood PhenotypeBlood Genotype Antigen on
RBC Membrane Immune (IgG)
Antibodies
Rh Positive
(85% of U.S.) + + or + -Rh antigenNone
Rh Negative
(15% of U.S.) - -No antigenMay Produce
anti-Rh
If Rh positive blood is accidentally given to an Rh negative recipient, the recipient will begin producing anti-Rh antibodies. Because of the time factor involved in building up a concentration (titre) of antibodies, the first transfusion may not cause any major problems; however, a subsequent transfusion of Rh positive blood could be very serious because the recipient will clump all of the incoming blood cells. The donor-recipient scenario with Rh blood types is summarized in the following table:
Donor Recipient Anti-Rh Antibodies
in Recipient's Blood
Rh Positive Rh Negative Will Produce
anti-Rh Antibodies
Rh Negative Rh PositiveWill Not Produce
anti-Rh Antibodies
Since Rh negative people may produce anti-Rh antibodies, Rh positive blood should not be given to an Rh negative recipient. Based upon the above table, Rh positive recipients can theoretically receive positive or negative blood, and Rh negative donors can theoretically give to Rh positive and Rh negative recipients. Therefore, the "universal donor" is O Negative, while the "universal recipient" is AB Positive.
Anti-Rh (immune-type) antibodies can readily pass through the placental capillary membranes. A serious potential problem called maternal-fetal blood incompatibility or Rh Disease could occur with a pregnant Rh negative mother who carries an Rh positive fetus. Leakage of fetal red blood cells (RBCs) into the mother's system through minute lesions in the placenta may cause her to produce anti-Rh antibodies. This could occur during the latter months of pregnancy or when the baby is delivered. Because of the time interval involved in producing a concentration (titre) of antibodies, the first Rh positive child may not be adversely affected. However, a subsequent Rh positive child may be at risk because the mother's anti-Rh can pass through the placenta, thus entering the fetal circulatory system and clumping fetal RBCs.
The medical term for this maternal-fetal condition is "erythroblastosis fetalis" because of the presence of nucleated, immature RBCs called erythrobasts in the fetal circulatory system. The fetus bone marrow releases immature erythroblasts because of the destruction of mature RBCs (erythrocytes) by the mother's anti-Rh antibodies. RhoGam®, a serum containing anti-Rh antibodies, is now given to Rh negative woman within 72 hours after giving birth to their Rh positive baby. The RhoGam® enters the mother's circulatory system and destroys any residual fetal positive RBCs that may be present in her system. This prevents her from producing anti-Rh antibodies. RhoGam® must be given after each Rh positive baby. In this scenario of erythroblastosis fetalis, the fetus must be Rh positive, the mother Rh negative and the father Rh positive. You can easily determine the exact genotype of the mother and fetus, but the father's genotype could be homozygous or heterozygous Rh positive. Rh incompatibility is summarized in the following table:
Rh Pos Father
+ + or + - XRh Neg Mother
- -
1st Rh Pos Child
+ -
Rh positive RBCs from the fetus enter the mother's circulatory system.
After several days, the mother begins to produce anti-Rh antibodies.
2nd Rh Pos Child
+ -
Anti-Rh antibodies from mother pass through placenta and enter fetal