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COMPATIBILITY TESTING

Dr. MOHAMMED H SAIEMALDAHR

BLOOD BANK

3RD MEDICAL TECHNOLOGY


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Out lineCollection and Preparation of Samples

Collecting Patient Samples

Donor Samples

Selection of Appropriate Donor UnitsTesting of the donor sample

Testing of the patient sample

Cross-match

Summary of Pre-transfusion Testing


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As the knowledge of new blood group system increased,so did the search for more sensitive pre-transfusioncompatibility testing methods. Pioneer blood bankersmixed the patients serum and the donors red cells and

observed for direct red blood cells lysis, agglutination, orboth. This became known as the major cross-match test.

The term compatibilitytest and cross-match are some

times used interchangeably, they should be clearlydifferentiated.


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The cross-match became part of a series ofpre-transfusion test known as compatibility testing. Thecompatibility test includes anABO and Rh groupingperformed on the donor and recipient samples, screeningof the donors and patients sera for unexpected

antibodies, and a cross-match.

The purpose of pre-transfusion or compatibility testing isto ensure the best possible results of a blood transfusion.

The transfused red cells will have an acceptable survivalrate, and there will be no significant destruction of therecipients own red cells.


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Collection and Preparation of Samples.

Positive Patient Identification

The major cause of transfusion associated fatalities havebeen clerical errors resulting in incorrectABO grouping

The most common cause ofclerical errors and thustransfusion accidents is misidentification of thepatient involved in the transfusion. Confusion in

identification of the patient when the blood sample wasdrawn a mixed up samples during handling in the lab,and error in identification of the patient when thetransfusion was given.


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To prevent collection of samples from the wrong patient,the blood request form must be used to confirm thepatients identity before phlebotomy is performed. Therequest form must state the intended recipients full

name, and unique hospital identification number.

Other information such as age and date of birth, address,sex, and name of requesting physician can be used to

verify patient identity further but is not required on theform.


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The patients wrist band identification must always becompared with the requisition form.

If the patient does not have a wristband or if the patientsidentity is unknown, some form of positive identificationmust be attached to the patient before collection ofsamples.


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Collecting Patient Samples

Hemolyzed samples can not be used for testing

because hemolysis caused byactivation of complement

Serum or plasma may be used for pre-transfusion testing.

Most blood bank technologist prefer serum because plasma

may cause small fibrin clots to form which may difficult to

distinguish from true agglutination.


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When a specimen is received in the lab, a blood banktechnologist must confirm that the information on thesample and requisition form agree.

All discrepancies must be resolved before the sample isaccepted, and if any doubt exists, a new sample must bedrawn.


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Donor Samples.

Donor testing samples must be taken when the full donorunit is drawn. Depending on the method used for testing,clotted sample, anti-coagulated samples, or both, areobtained.

Donor information and medical history card, the pilotsamples for processing, and the collection bag must allbe labeled with the same unique number code before

starting the phlebotomy, and the numbers must beverified again immediately after filling.


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Donor and recipient samples must be stored for aminimum of 7 days following transfusion.

The samples should be stoppered and refrigerated at 1-6C, carefully labeled, and adequate in volume so thatthey can be re-evaluated if the patient experiences anadverse response to the transfusion.


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Compatibility Testing Protocols.

Selection of Appropriate Donor Units.

In almost all cases,blood and blood components of the

patients own ABO and Rh group should be selected fortransfusion.

When blood and blood components of the patients type

are unavailable or when some other reason precludestheir use, units selected must lack any Ag against whichthe patient has a significant Ab.


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When transfusion of an ABO group different from therecipient must be given, packed red cells must be usedrather than whole blood which contains plasma Abs thatare incompatible with the patients red blood cells.

Group O packed red blood cells can be safely used for allpatients, however, conservation of a limited supply ofgroup O blood should dictate its use for patients of other

AB types only in special circumstances.


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If ABO-specific blood is not available or is in less than adequatesupply, alternative blood groups are chosen as summarized in thefollowing table;

Patient s BG Alternative BG given as packed cells

O NONE

A O

B O

AB A, B, Oonly one of the three should be used for a given patient


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Rh-negative blood can be given to Rh-positive patients,however, good inventory management again shouldconserve this limited resource for use in Rh-negrecipients.

If Rh-neg units is near expiration, the unit should begiven rather than wasted.


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Rh-pos blood should not be given to Rh-neg women ofchildbearing age.

Transfusion ofRh-neg male patients and female patientsbeyond menopause with Rh-pos blood is acceptable aslong as no performed anti-D is demonstrable in the sera.


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Compatibility Testing Protocols.

Testing of the donor sample.

According to the Code of Federal Regulation (CFR) andtheAmerican Association of BB (AABB) standards,ABOand Rh grouping (including a test for weak D) and tests

intended to prevent disease transmission must beperformed on a sample of blood taken at the time ofcollection of the unit of blood from the donor.

A screening test for unexpected antibodies to red bloodcell Ags is required byAABB standards on samples fromdonors revealing a history of prior transfusion orpregnancy.


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Testing of the donor sample

The transfusing facility is required by AABB standards toconfirm theABO cell grouping on all units and Rhgrouping on units labeled Rh-neg.

Tests forweak D (Du) are not required to be reported.The transfusion facility does not need to repeat any othertesting procedure.


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Testing of the patient sample.

A record of all results obtained in testing patient samples must bemaintained.

Identification number should be assigned each time a patient isadmitted for treatment.

Any discrepancies between previous and current results must beresolved before transfusion is initiated.

A new sample should be collected from the patient, if necessary toresolve the problem.

ABO and Rh grouping results should be included in the file.

Also, notations concerning unusual serologic reactions and theidentity of unexpected Abs in the patients serum should beincluded.


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ABO and Rh grouping and Ab screening of the patientsserum can be performed in advance of or at the sametime as the cross-match.

If the patient has had a transfusion or has been pregnantwithin the last 3 months or if the history is unavailable oruncertain, the sample must be obtained from the patientwithin 3 days of scheduled transfusion.


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ABO Grouping.

Determination of the patients correct ABO group is themost critical pre-transfusion serologic test.

If the cell and serum grouping results do not agree,additional testing must be conducted to resolve thediscrepancy.

If the patients ABO group cannot be satisfactorydetermined and immediate transfusion is essential,group O packed red blood cells should be used.


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Rh Grouping.

Rh grouping is performed using anti-D blood groupingserum. Tube or slide tests should be performedaccording to the manufactures directions for thereagent, which may or may not include the use of asuitable diluents control.

Control must be run in parallel with Rh grouping testsperformed on patients samples, to avoid incorrectdesignation of Rh neg, patient as Rh positive.


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Direct antiglobulin test (DAT) should be performed onthe patients red blood cells to determine whether uptakeof autoantibody, (alloantibodies, if the patients has beenrecently transfused) is responsible for the positive

control result.


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If the Rh group of the recipient can not be determinedand transfusion is essential, Rh negative blood should begiven.

The test for Du is unnecessary when testing transfusionrecipients. Individuals typing as Rh neg in direct testingshould receive Rh-neg blood and those typing as Rh posin direct testing should receive Rh pos blood.

As Du are considered Rh pos and may receive Rh posblood during transfusion.


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Antibody Screening.

The patients serum or plasma must be tested forunexpected Abs.

The aim of the Ab screening test is to detect as manyclinically significant Abs as possible.

Clinically significant Abs refers to Abs that are reactive at37C or in the DAT or both and are known to havecaused a transfusion reaction or unacceptably shortsurvival of the transfused red blood cells.


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Abs Regarded as always being potentially clinicallysignificant

ABO Rh Kell Duffy Kidd S s U

Abs that may sometime be clinically SignificantLea p Lua Lub Cartwright.

Abs that rarely, if ever, are clinically significant

Leb Chido/Rodgers (Cha/Rha) York, Sd Xg& Bg


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Correct ABO grouping results are much more critical totransfusion safety than Ab screening.

Most Abs, other than anti-A and anti-B do not causesevere hemolytic transfusion reactions. Thus the vastmajority of patients would not suffer grave consequencesif transfused with blood from ABO group compatibledonor without the benefit of Ab screening tests.


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Detection of unexpected Abs is important, however, forthe selection of donor red blood cells that are likely tosurvive maximally in the patient circulation.

Weakly reactive Abs that are capable of reacting withtheir Ags at 37C can cause decreased survival oftransfused incompatible red cells.


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Because large numbers of Ab molecules are present inthe patients circulation compared with the number ofred cells in a unit of blood, incompatible donor cells arehighly vulnerable to destruction by patient Abs.

Abs screening offers several advantages over directcross-matched testing for detection of Abs;

1- Testing is performed using selected group O red cellsthat are known to carry optimal representation ofimportant blood group Ags.


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2- Testing can be performed well in advance of theanticipated transfusion, allowing ample time foridentification of unexpected Ab and location of suitabledonor units lacking the corresponding Ag.

Methods used to detect Abs in patients sera mustdemonstrate all significant coating, hemolyzing, andagglutinating Abs active at 3 7C.


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Cross-match

The two main functions of the cross-match test can becited as,

I- It is a final check of ABO compatibility between donorand patient.

2- It may detect the presence of anAb in the patientsserum that will react with Ags on the donor RBCs butthat was not detected in the Ab screening because thecorresponding Ag was lacking from the screening cell.


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Cross-match

Major and Minor cross-match tests

Major cross-match test, consisting of mixing the patientsserum with donor RBCs.

Minor cross-match test, consisting ofmixing the donorsplasma with patients RBCs

The minor cross-match test has been completelyeliminated in most blood banks, because donor samplesare screened beforehand for the more common Abs.


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Cross-match

Method for major cross-match tests.

Cross-match methods can be categorized by the testphase in which the procedure ends.

Immediate spin (IS) cross-match (Abbreviated

Cross-match)

When no clinically significant Abs are detected nor arethere previous record of such Abs, a serologic test todetect ABO incompatibility is sufficient.


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Cross-match

In IS (the patients serum with donor cell are centrifugeimmediately) absence of hemolysis or agglutinationindicates compatibility.

False reaction may be seen in the presence of other ISreaction (auto -I). In patient with hyperimmune ABOAbs, when the procedure is not performed correctly(delayed in centrifugation or reading) when rouleauex is

observed, or when infants specimens are tested.


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Cross-match

Antiglobulin Cross-match

The procedure begin in the same manner as the IS cross-match, continues to 37C incubation and finishes withAHG test.


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SUMMARY


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SUMMARY

PRE TRANSFUSION TESTING

Is to provide safe, compatible blood for transfusion to

each individual patient. The steps necessary for safetransfusion are:

1. Accurate ABO and Rh typing of the patient.

2. Accurate ABO and Rh typing of the donor.

3. Screening tests for antibodies in the donors andpatients serum.

4. In the presence of patient antibodies, selection ofappropriate units for each patient.

5. Compatibility Testing - (Major)

6. Accurate completion of paperwork and labels


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Compatibility Testing

Each compatibility test is a unique experiment in whichan unknown (patient) serum and (donor) red cells aretested for the detection of unexpected antibodies which

are directed against antigens found on the cells. Negativeresults indicate compatibility. This is one of the mostimportant tests performed by a transfusion service.


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The purposes of compatibility testing are:

1. To detect irregular antibodies in the recipient serumthat are directed against the donors cells.

2. To detect errors in ABO grouping.

3. To detect errors in labeling, recording, or identifyingdonors or recipients samples.


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Compatibility testing does not:

1. Ensure normal survival of donor red cells.

Prove that donor and or recipient serum is free ofantibodies. Prevent immunization of the recipient.

Detect ALL ABO typing errors.Detect errors in Rh typing of either recipient or donorunless the recipients serum contains an Rh antibody.

Detect ALL error of identification.

Pre-transfusion testing of the recipient must include anABO and Rh typing, antibody screen, and a cross-matchwith all donor units.


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Patient red cell withD Ag.


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If Rhve do


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