Notes on Cross Matching

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At the completion of this lesson, you should be able to:

State the basic purpose of a crossmatch protocol

State the outdate of a crossmatch and explain why this is necessary

Describe the benefits of a crossmatch

Discuss the limitations of compatibility testing

Discuss the steps in compatibility testing and explain the purpose of each

List 5 items that should be a part of a patient’s blood bank records

Explain what a Type and Screen consists of, and when it would be used.

State the major purpose of an immediate spin crossmatch

Explain when a Coombs crossmatch would be done versus an im¬mediate spin crossmatch

Describe what additional testing must be done when crossmatching a patient with a clinically significant antibody

Explain what an electronic crossmatch is

List three criteria that must be met to perform an electronic crossmatch


The crossmatch protocol goes by several different names - pretransfusion testing, compatibility testing, the type and cross, or the T and C. Basically, the crossmatch protocol is a series of tests performed on the patient’s blood before transfusing to help ensure that the donor blood will be safe for the patient. Once donor blood is crossmatched for a patient, it is only good for three days before a new sample must be drawn and the crossmatch repeated. This is because the patient could be making new antibodies at any time - especially if he or she has been recently transfused or pregnant (within the past 90 days) - and the previously compatible blood may now be incompatible.

enefits and Limitations


Detects major ABO incompatibilities - One of the major purposes of a crossmatch is to detect major ABO errors, either when typing the patient or when selecting donor blood. For example, if you mistakenly type a patient as an A when he is really a B, and then try to crossmatch group A donor blood, the donor unit will be strongly incompatible. The same thing would happen if you correctly typed him as an A, but then erroneously tried to crossmatch a group B donor unit for him. Strong incompatibility at the first phase of the testing suggests a major ABO error.

Identifies clinically significant blood group antibodies - The other major purpose of the crossmatch is to identify any clinically significant blood group antibodies other than ABO that the patient might have, and to ensure that the donor blood lacks those antigens.

Safe, fast, accurate - The crossmatch protocol should be designed for speed and accuracy - to find the safest blood that is reasonably possible for the patient as soon as reasonably possible. It is not meant to find and identify every single antibody that might possibly exist in the patient’s plasma, and it is meant to bypass the clinically insignificant antibodies.


Errors in patient identification - The crossmatch is not foolproof. The crossmatch may not detect errors in patient identification, unless a previous record of the patient’s blood type exists. For example, if blood was drawn from one patient (the incorrect one) into a sample tube labelled with a different patient’s name (the one the crossmatch is intended for), and these patients were two different blood types, the blood bank would provide blood that was compatible for the incorrect patient - not the patient for whom the transfusion was intended. There could be a fatal hemolytic transfusion reaction if that blood were then transfused to the patient whose name was on the sample tube, but whose blood was not in that tube.

Minor ABO errors - The crossmatch will also not detect compatible ABO errors. For example, if you typed the patient as an O when he was really an A, and then crossmatched group O blood for him, it would be perfectly compatible, but it would be the wrong blood type. Similarly, if you typed him as...
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