Skills: 20 points
Blood bank personnel are responsible for providing serologically compatible
blood within an appropriate time frame. A crossmatch (compatibility test) is
performed for patients who need replacement of their blood volume due to anemia
or active, massive bleeding.
Compatibility testing includes a number of blood bank procedures performed before a transfusion to ensure the proper selection of blood for the patient. These procedures should include the following:
Scientific and technical advances in blood group immunology have made the transfusion of blood a relatively safe procedure, but serious adverse effects of transfusion still result because of human error. Only individuals who understand the importance of blood bank protocols and adhere to them should be allowed to collect patient samples or perform tests. Failure to concentrate completely and use of careless techniques in performing laboratory tests directly endanger the life of the patient.
The purpose of crossmatching is to prevent the transfusion of incompatible cells. Testing of the recipient's (patient) serum with donor cells ("major crossmatch") is required because it is the best available way to detect antibodies in the patient serum that might damage transfused red cells and cause hemolytic transfusion reactions.
When performed properal, a compatible crossmatch will:
The crossmatch has many limitations. A compatible crossmatch will not:
Standards requires that tests for serologic incompatibility employ methods that demonstrate ABO incompatibility, detect clinically significant antibodies active at 37C, and include the antiglobulin tests. The patient specimen must be less than 72 hours old for compatibility testing so that it represents the current immunologic status of the patient.The major crossmatch involves testing the patient's serum with donor cells to determine whether the patient has an antibody which may cause a hemolytic transfusion reaction or decreased cell survival of donor cells. Of greatest importance is detection of ABO incompatibilities. ABO problems quickly become apparent when the mixture of patient's serum and donor cells is examined after centrifugation (immediate spin crossmatch). Unexpected cold reacting antibodies may also become apparent at this step, but once identified as such, they are usually considered insignificant.
The crossmatch is incubated at 37C to detect clinically significant agglutinating or hemolyzing antibodies. After incubation and washing, antiglobulin serum (Coomb's serum) is employed to detect antibodies that have attached to cells without causing agglutination (sensitization).
Additional solutions such as albumin, polymerized albumin or low ionic salt solutions (LISS) are frequently employed to increase the sensitivity of the crossmatch or to reduce the incubation time. By lowering the ionic strength or increasing the dielectric constant of the test medium, these solutions increase antibody uptake and enhance the strength of the antigen-antibody reaction.
An antibody screen is performed along with the major crossmatch. The antibody screen is important in detecting weak antibodies which may only react with the homozygous screen cells or to detect antibodies directed against antigens present on the reagent screen cells but not present on the donor cells.
The minor crossmatch involves testing the patients cells with donor plasma to determine whether there is an antibody in the donor's plasma directed against an antigen on the patient's cells. Since all donors are routinely screened at the collection facility for irregular antibodies this procedure is no longer routinely performed. There may be rare instances when this procedure may need to be performed so be familiar with it.It cannot be stressed enough that complete concentration and good technique must be used in blood bank procedures. Incorrect identification of specimens or materials or incorrect recording of results or interpretations cause false positives, false negatives and total disaster!
Selection of Blood for Transfusion
Whenever possible the blood selected for crossmatch should be of the same ABO and D group as that of the recipient. However, there are instances when it is acceptable or even advisable to transfuse red blood cells of a different ABO group, provided that they are compatible. For example:
D positive individuals may receive D negative blood, although D negative units should be reserved for D negative patients. But a common sense approach to blood usage should be maintained. If you have an A positive "sure give", and you have 2 units of A negative expiring soon, it is a better use of the blood resources to give the 2 D negative to prevent their expiration. You would not make this decision on your own, but would confer with your coworkers or supervisor.
D negative recipients should always receive D negative blood unless a life threatening situation arose. The doctor would need to sign a release form agreeing to the transfusion of D positive blood to this individual.
Choice of Blood When Group Specific Blood is Unavailable
When blood of the recipient's ABO group is unavailable, transfusion with an alternate group, as shown, is acceptable but must be administered as red blood cells. Note that for AB individuals the Second Choice lists group O as the next logical choice. Group B blood is relatively uncommon, you would not wish to deprive group B patients of type specific blood, so it makes more sense to choose group O, which is usually in abundant supply.
|Patient ABO Group||First Choice||Second Choice|
|AB||A||O or B|
|A2B with anti-A1||A2||O or B|
Group AB positive is considered to be the universal recipient for red cell transfusion. Due to their lack of ABO antibodies they will be compatible with all red blood cell types. For the transfusion of red blood cells group O negative is the universal donor since it lacks all ABO and D antigens. In an emergency situation group O negative red blood cells would be issued until a patient sample could be tested.
For plasma components group O is the universal recipient, since they have all ABO antibodies present all plasma products will be compatible. Group AB is the universal donor for plasma products since they lack all ABO antibodies.
It is critical that you have a basic understanding of universal donors and recipients. In an emergency situation you may need to utilize these concepts to transfuse massively bleeding patients and you must know what your options are to provide the safest products for the situation at hand. You must also have a sound understanding and use a common sense approach any time you must provide blood of a different type to a patient.
|donor 2 cells||O||O||O||O|
|donor 1 cells||O||O||O||O|
|clot||patient cell O||O
|A cells O||B cells O||S1 O||S2 O||S3 O||Xm 1 O||Xm 2 O|
Interpretation of Results
A. If all tubes have remained negative throughout the crossmatch procedure, and the check cells have checked, the antibody screen is "negative" and the units are interpreted as "compatible", record as "comp" on your sheet.
B. Antibody screen is positive, units may be compatible or incompatible (record as "incomp" on sheet):
C. Antibody screen is negative, but one or more units appear incompatible perform a DAT on the unit:
Other more complex problems may arise when doing a crossmatch, such as all tubes in the crossmatch procedure giving positive reactions. This is usually due to nonspecific warm autoantibodies or multiple antibody specificities present in the patient sample. Extensive testing would need to be performed to resolve the problem.
If other problems occur other than those listed, consult your reference books which should be present in the laboratory.
Next week, along with the study questions, you must turn in a condensed procedure written on one index card. This is to be written in a simplified manner to aid you in performing this procedure.
Prepare cell suspension, use serum tube as balance tube
While RBCs and serum tubes are spinning, label ALL tubes
Add patient serum and reagent serum to ALL tubes
Add patient cells to forward, and reagent cells to reverse typing tubes
Spin forward/reverse tubes, record patient information from clot tube onto result sheet
Read, record forward/reverse reactions, interpret, obtain appropriate donor units from blood bank
Prepare donor cell suspensions, while these are spinning drop reagent screen cell in approprirate tube as well as patient cells from clot tube into retype tubes
Drop donor cells into appropriate forward AND crossmatch tubes
Spin screens AND crossmatch tubes, read and record.
ADD ALBUMIN TO SCREEN AND CROSSMATCH TUBES AND
PLACE IN 37C WATER BATH.
Spin, read and record patient repeat and donor forward types, incubate D and D ctrl tubes if patient/donors are D negative.
After incubation spin and record SC and XM tubes
Wash 3Xs (incuding D and Dtrl if D=), add AHG, read macro and micro, record
Add check cells, spin, read and record
If no agglutination in check cell tubes, START OVER
You will need to word process the study questions. The easiest way is to copy the question (control-c) then paste (control-v) into your word processing program.
|Crossmatch Phase||Antibody Class Detected|
|Blood Group||First Choice||Second Choice|
|A2B with anti-A1|