Creatinine: all the different places that you
might have to run to, to look for the relevant
information of creatinine. It's all here.
What does that mean? What is a normal mechanics
of creatinine? What does it mean to you in
terms of interpretation of creatinine so that
you can help you diagnose your patient? Remember
this is going to be part of your laboratory
investigations and is it the only thing that
you are going to use to confirm. No, but it
is a darn important one. What is creatinine?
We will begin. The breakdown
product of the skeletal muscle and how often
does that occur? All the time constitutively.
Keep that in mind. Constant release into the
blood stream. Once again because your muscles
are breaking down you get it into your bloodstream.
Remember as to what the normal levels of creatinine
is? Well, I want you to think of 6 and 12. You
double 6 and you get 12. It is 0.6 to approximately
1.2. Keep it simple. There is so many different
things that you need to memorize, right? And a couple
of things here and perhaps it may help you
keep it mind, but 0.6 to 1.2. How does the
kidney handle creatinine? Well, I want you to go
into the plasma. I want you to go into afferent
arteriole. I want you to arrive at the glomerulus
and I want you to filter through. Does creatinine
get filtered? Is it small enough for it to
get filtered? It is. So it gets filtered. Correct. Okay? Next.
As it gets filtered, you will continue through
your glomerular capillaries and you end up
on the efferent arteriole, are you there? and you continue
through the peritubular capillaries. We call
this what? vasa recta and you tell me what should
happen around the PCP, proximal convoluted tubule
and its communication with the peritubular
capillary. Are you with me? Are you there?
Next well what kind of mechanisms are taking
place between the PCT and the peritubular
capillary? Two major mechanisms. One
would be secretion and one would be reabsorption. Right?
So of the two which process is creatinine
following? Secretion. What does secretion
mean? Secretion means you are always, I don't care
where you are. What does that mean?
You could be in the intestine. You could be
here in the nephron. Secretion always means
you are secreting into the lumen. What is
in the lumen here? The PCP, proximal convoluted
tubule and the lumen is the urine. Creatinine
will be slightly secreted. Is it filtered?
Yes. Is it secreted? Yes. Keep that in mind.
It is not reabsorbed. Is that clear? What
does the reabsorption mean? Once again you
could be in the GI or you could be in the
nephron. Those are two major organ system
where secretion, reabsorption is a major function.
You want to keep these in mind. Many many
pathologic conditions in which there might
be excess reabsorption or excess secretion.
You will see as we walk through many differentials.
Creatinine is not reabsorbed. It doesn't come
back into the blood. That is important. It
is only slightly secreted. So therefore when
something gets filtered and it gets cleared,
what does cleared mean? It is what you are
actually analyzing when you get the urine
out meaning to say literally and I am going
to be rather dramatic here in the toilet.
That is clearance. There is a difference between
clearance and filtration. Filtration is you
are moving from the glomerular capillaries
from the afferent arteriole tuft of capillaries
and into the glomerulus. That's it. That
is as far as filtration goes. Is that clear? Haha, no pun
intended. Clearance means what you are actually analyzing
in the toilet, which you actually excreted.
My point is this. So if creatinine gets filtered,
does it do that? Yes. Does it get reabsorbed?
No. Does it get secreted slightly? Which means
that clearance would be greater than or less
than or equal to GFR. That is your next big
question. Think about that. Close your eyes.
Listen to what I am saying. Conceptualizes
right now. Clearance will be greater than
GFR. What does that mean Dr. Raj? It means
that because of slight secretion would be an
overestimate of what is actual filtration?
Now how are you as a clinician going to use
all this information. Well, there is a couple
of tests that you would do with creatinine,
which we will then use or you will then use
in practice to measure or analyze or assess
the function of your kidney and there are
two ways in which you can then use creatinine
to assess the functionality of the kidney.
You can either use what is known as creatinine
clearance, which is extremely cumbersome or
you can use the surrogate marker meaning you
will then measure the amount of creatinine
in your plasma and how do you do that? With
a blood test. Now, what is the 0.6 to 1,
we were talking about that level? Is that
the measurement that you are going to find
as a marker in your blood or is that part
of what is known as your creatinine clearance?
You tell me that is your plasma, isn't it?
So you can measure the 0.6 to 1.2 is a very
quick general functioning assessment of the
kidney that you are going to get from the
blood. Keep that separate from what we see
here. This is the creatinine clearance. So
what does that mean? You are going to give
your patient a container and you are going
to tell this patient for approximately 24
hours to urinate in that container. Does that
seem rather cumbersome? Sure. Does that mean
that you are dependent upon the compliance
of the patient? Yes, you are. A lot of factors,
a lot of ifs. But if done properly, it is
a pretty good marker once again of renal function.
Now because of that slight secretion, we just
said that it would be greater than GFR. Understand
that point. Do not just breeze through that.
GFR is equivalent to filtration. Clearance
is what you are actually evacuating from your
body. Because of slight secretion, I repeat
once again that creatinine has greater
clearance than GFR. Used as an
approximation of GFR. What is CrCl? Creatinine
clearance. How do you assess this test? This
is not the blood test. This is the one in
which you are measuring how much creatinine
is actually being cleared.