Episode 060: Heme Consults Series - Fundamentals of Transfusion Medicine
We are taking a small pause from our breast cancer series to discuss an important topic that is so critical to understand for clinical practice, no matter what discipline of medicine you are in: the fundamentals of transfusion medicine. This topic often shows up quite frequently on board exams, as well. In this episode, we talk about terms such as “type and screen” and more.
How do we define what someone’s blood type is?
Based on the presence of antigens on the red cell surface; divided into the major and minor antigens
Major antigens
A
B
O
Minor antigens (there are actually many more than what is listed here!):
Rh (most immunogenic); often denoted as +/-
Kell
Kidd
Duffy
MNS system
This is important because patients will have naturally occuring antibodies against antigens
For instance, patients with Type A blood have naturally occuring IgM antibodies against the B-antigen, even if they had never been exposed to type B blood.
Patients can also develop antibodies against minor antigens, which can potentially result in the formation of antibodies, too.
What does it mean when we request a “type and screen”?
ABO/Rh(D) Typing - what blood group TYPE does the patient have?
ABO:
How do we do this? Coomb’s test!
Forward Typing (AKA “coomb’s test” AKA “direct antibody test” AKA “DAT”)
What you want to know: If you have the patient’s blood cells, but you don’t know what antigens they express. How to solve this?
How is this done?
Mix patient’s RBCs one at a time with Anti-A, Anti-B (IgM)
If there is a reaction AKA agglutination (since IgM), then that antigen is present on RBC cell surface
Based on the pattern of agglutination, you can tell the ABO type
Example: Patient’s RBCs react with Anti-A, but not Anti-B. Therefore, they have ABO type A.
Reverse type: You want to confirm your finding.
This time you take the patient’s serum (which has antibodies but no RBCs) and mix it with test blood with KNOWN antigens
If you add test A blood and there is agglutination with the patient’s serum, then there are Anti-A antibodies.
Remember that means that their RBCs should not have A antigen on them otherwise they would attack their own cells!
Example: Take the patient’s serum from example above. If you mixed it with KNOWN A-type RBCs, you would NOT get a reaction. But if you mixed with B-type RBCs, you WILL get a reaction.
Rh(D)
Because Rh antigen is still immunogenic, that is checked, too
Only forward typing because you either have Rh or you don’t
Take patient’s RBCs and mix with Anti-D.
If there is a reaction, then they have Rh antigen
Screen: SCREENING for antibodies that may be present
Take patient’s serum (which has any potential antibodies in it) and take KNOWN Type O blood (which has no antigens on) with a variety of antigens expressed, including combinations of the minor antigens.
You are wanting to ensure that there is no reaction, because that would mean the patient has antibodies in their serum.
If this is positive, then they go on to do an identification of the antibody
What is “crossmatching” then?
Once you have typed-and-screened, you know the patient’s blood type and any antibodies they may have, so then you want to find blood that is compatible (AKA the same)
Cross match is when blood from the patient is mixed with donor blood and you want to ensure there is no reaction.
When would we expect there to be discrepancies in the forward and reverse typing?
Patients who are heavily transfused (massive transfusion protocol)
Critically ill patients
Stem cell transplant patients who have received a transplant from an ABO mismatch patient
Newborns
When would we expect to see discrepancies in the antibody screen?
This is when the patient’s own serum causes the patient’s own washed RBCs to agglutinate in the absence of anything else (there’s something going on that is not supposed to!!)
When can we see this:
Hemolytic transfusion reactions
Patients who received lots of blood (massive transfusion protocol)
Autoimmune hemolytic anemia
Rouleaux formation in myeloma can look like agglutination
Drug-induced antibodies (penicillins, ampicillin, cephalosporins)
Anti-D Ig (Rho-Gam)
IVIG
The crew behind the magic:
Show outline: Ronak Mistry
Production and hosts: Ronak Mistry, Vivek Patel, Dan Hausrath
Editing: Resonate Recordings
Shownotes: Ronak Mistry
Social media management: Ronak Mistry
Remember:
Whole blood: contains everything
Plasma: all the proteins in circulation
Serum: plasma minus clotting factors
