thus your clearance is greater than GFR. Understood?
Now to correlate with GFR. What kind of things
that you want to keep in mind. As you said,
as one gets older, then your GFR starts dropping.
Your renal failure per se but you always want
to keep that mind because you do not know
as to what the patient has been exposed to. Was
it diabetes mellitus? What is it drugs that
were nephrotoxic. Regardless as the patient
gets older, then their creatinine clearance
is going to drop by 1 milliliter per minute
after the age of 50. What does that mean to
you? Normally speaking in older patient above
the age of 50, what do you expect your plasma
creatinine levels to be? On the higher side
or lower side if your GFR starts dropping
after the age of 50? Obviously increased okay.
So if by chances you are reading the lab and
interpreting it and you are attending or boards
or whatever asking you, what does this mean
to you? Keep in mind that your creatinine
levels plasma will be elevated at the age
of 50. Useful in detecting renal dysfunction.
Okay now. You want to spend a little bit time
here and take a look at what the creatinine
clearance formula is measuring and the bottom
line is this though. You definitely want to pay attention.
UV/P. Take a look at U. What is U? That is the urine
concentration, milligrams per deciliter. It
is important that you pay attention and highlight
in your head milligrams over decilitres being
the unit times V. That is the flow rate and
that would be once again millilitres per minutes.
Units are important every once in a while
you will get an equation and you are responsible
for calculating it and if you keep the units
in mind, trust me it will you help you a lot.
What is this for? This is the equation for
clearance. Think UV, think ultraviolet if
that helps you in the numerator. So on top
we have U x V. What is U? Urine concentration
x V the flow. Draw a line a slash so it is
divided. So in the denominator, you will have
the plasma. It is UV/P. If that helps you
remember. The P will be the plasma concentration
of creatinine and that will be milligrams
per deciliter and there you have it as being
the equation for clearance in general. When
you are going to play around with this quite
a bit all that you do at this point is learn
the big formulas. The big formulas from cardiology,
the big formulas in nephrology and all you
do is to start manipulating it and once you
do, you will get the answer. No doubt.
So here what are we looking for clearance wise?
We are looking for the clearance of creatinine
and we have UV/P and once we figure all this
out well you get the clearance of that particular
agent. What is the agent here? Creatinine.
So at some point in time maybe I am asking
the question about clearance of some other
substance and once they do use the same formula
and you substitute the creatinine with the
other substances that they might be asking
about. Normal adult creatinine clearance.
97 to 137. What is that normal? In general
creatinine clearance, less than 100 is abnormal.
This is not the same thing as plasma creatinine.
Plasma creatinine is what was measured in
the blood. Where we are measuring this creatinine?
What has been cleared? So less than 100. You
want to suspect. Oh! the patient is having
a pathology of some sort. There is some kind
of renal failure. Less than 10. Oh! boy absolutely
look at this. Absolute renal failure, less
than 10. That means that the kidney is not
filtering anything. If its not filtering anything,
then how in the world are you going to clear
anything? You're not? It is going to much much
much less. Now as a caveat, we talked about
elderly patients. It is absolute imperative
that you, before you begin administering any
drugs such as aminoglycosides, gentamicin
what not, aminoglycosides antibiotics. It
is absolutely imperative that you figure out
the renal function for us because if that
patient is not able to properly evacuate that
drug from the kidney and especially if that
drug is known to be a nephrotoxic agent, then
you are going to then bring about acute renal
failure and you don't want that specifically
acute tubular necrosis. At some point when
we further get into nephrology, we will start
talking about renal failure. We will then
divide acute and chronic renal failure. Under acute renal
failure we will talk about acute tubular necrosis.
Under acute tubular necrosis, we will talk about
two major divisions. One will be ischemic and one
will be nephrotoxic with things like drugs.
It is important that you figure out the proper
renal function of an elderly patient which
you expect to be on the higher side in plasma
creatinine and the creatinine clearance will
give you the actual renal functionality so
that you can adjust the dose of the nephrotoxic
drug so that you don't kill the kidney of
the patient. Are you putting things together
now? It is all about understanding the physio,
understand the normal, how to use the formula
that has been given to you and then obviously
the clinical application and how you will
then apply this in your clinical wards, clinical