Okay,
let’s talk about the Coombs test.
The Coombs test is done to check whether there is
an autoimmune component to our anemia.
We see this fairly frequently where patients are having antibodies
in babies that might be mom’s antibodies that have crossed the placenta
and attacked our child’s red blood cells
or in older children, they may just have autoimmune hemolytic anemia.
So the Coombs test tells us if there are antibodies and if there are,
what those antibodies are attacking.
If there are antibodies as the direct Coombs
and what those antibodies attacking is the indirect Coombs.
These are confusing
and I want to go through these tests individually
because it often shows up on your exam.
So the direct Coombs detects for antibodies that are
actually attached to the blood cell right now.
And the indirect takes the antibodies out of the patient,
leaves their own red cells in the dish
and then we look at those antibodies and see what are they attacking.
Okay.
Here are patient’s red blood cells.
This patient is having an autoimmune hemolytic anemia.
Antibodies are sticking to this patient’s cells
and these antibodies are sticking to vary a variety of proteins on those cells.
Now, this patient is going to have cross-linking
of those red blood cells and those complexes.
So these red blood cells will naturally clump together.
When I do a Coombs test, if the blood clumps like that, I can say,
“Yeah, I think there are antibodies.”
Now if I suspect there are antibodies, I will do the indirect Coombs.
Here’s a red blood cell in a patient with an autoimmune hemolytic anemia
and this patient has both A and B proteins on their blood.
They are type AB.
Okay.
And what the heck, let’s make them AB positive.
So they have an Rh which is the positive thing on there
and they have A proteins and they have B proteins
and these are all in the surface of that red blood cell,
so this is AB positive individual.
This is sad because this patient is now going to get an autoimmune hemolytic anemia
where antibodies directed at the Rh factor are sticking.
Antibodies against the A protein are sticking
and antibodies against the B protein are sticking.
This is a bad scene for this patient.
What we’re going to do with this blood now, however,
is we’re going to take all of their blood
and we’re going to separate out the red blood cells,
leaving only the antibodies that are floating in the patient’s serum.
So now we have just the patient’s serum.
We’re going to take their serum and we’re going to isolate it
and we’re going to now put it against a certain number of predonated cells.
So person number one happens to have A positive blood.
Guess what will happen.
All those A antibodies are going to go up and bind to that volunteer’s blood.
Now, we will put in some B cells and the B’s will go and attack the blood.
In fact, whatever the protein, it will attack the blood.
Now, here’s a donator with another protein, “X”.
I don’t know what X is, you can make it up,
but the point is this patient does not have any anti-X antibodies
so nothing is going to stick to that X.
So then, what I do is I take this donor’s blood and I put it in a dish.
Here’s the dish
and I’ve got the first donor on the top left is an AB positive person.
The next one is an O positive person.
The next one is AB.
The next one is B, et cetera.
They also have other things,
other proteins like that X1 and so, every single pattern in there is represented.
Every protein by this donor is represented.
Now I take our patient with autoimmune hemolytic anemia and I put it in there.
Let’s say that this patient had anti-A antibodies.
All of these dishes would see clumping, but the other dishes would not.
So when I look at this array and I see this pattern,
I can say, “Yup, this patient has anti-A antibodies in their serum.”
I have essentially figured out what this person is attacking.
Why am I focusing on this?
Why is it so important?
Well if this patient used to be transfused because their blood is getting so low,
I assure and this is their pattern, I know I can’t put in A blood.
But if this were their pattern, I probably would be okay to put in B blood,
because look, the A’s are all bound and B’s aren’t.
That’s how we determine what blood is safe to transfused into these individuals.