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
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.
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.
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
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.