00:01
Welcome to our video series
on interpreting lab values.
00:04
In this video, we're going to
take a look at serum creatinine
and calculation of the eGFR,
that means an estimate of the
glomerular filtration rate.
00:14
So let's give a quick review
of what serum creatinine is.
00:18
It's a chemical waste product
and it's produced by
muscle metabolism.
00:22
Men have a little bit
higher level than women do
but that's because
they usually tend
to have a higher amount
of muscle in their body.
00:30
Okay, we know it's
here in creatinine is
we know that it's a
little higher for males
than it is for females
but what else does
it help us do,
well it helps us assess
renal or kidney function
if your kidneys are impaired
that'll lead to
an increased level
of creatinine in the blood.
00:47
But serum creatinine can
also help us estimate
how well the kidneys
are filtering
right down to the glomeruli.
00:54
GFR is the glomerular
filtration rate.
00:58
Now, that means how much blood
is Passing through the glomeruli
for each minute.
01:03
So the serum creatinine helps
us assess renal function.
01:06
It also helps us with the GFR.
01:09
Now the reason it can do that is
because creatinine is usually produced
at a fairly constant rate
and it clears the kidneys without
being reabsorbed that much
so, super smart people
figured out that we can do some
fancy math with the serum creatinine
and get a number that estimates
the glomerular filtration rate.
01:28
Now, you might wonder why we
don't measure the GFR directly.
01:32
Let me help you
understand a little bit.
01:34
The estimated GFR is
this formula that uses
the patient's serum creatinine their
age, their sex, and their race.
01:42
That's a lot of variables and I'm really
glad we don't have to do the math,
but it's kind of a clue to let
you know that a patient's GFR
can be impacted by
not only their sex,
we talked about
that with creatinine
but also their age
and their race,
so that's what the form
they will take into account.
02:01
We don't measure
the GFR directly
because it's way too
cumbersome to do that.
02:07
Now there are some special markers
that are difficult to pronounce
and to spell not even going
to go into those here.
02:13
Just take my word for it.
02:15
It's way too cumbersome to do
that in a clinical setting.
02:18
That's why we use
the serum creatinine
and the fancy math
to give us an estimate of how
those glomeruli are functioning.
02:26
Now there's some unusual things
about how a GFR is reported.
02:30
GFR greater than 60,
greater than or equal to
60 is considered normal.
02:36
Okay, so you probably
won't even see a number
reported if your patients GFR
is greater than or equal to 60.
02:44
When that glomerular
filtration rate drops below 60.
02:48
That's when you'll start
to see those numbers appear
on your patients lab work.
02:52
Now keep in mind differences between
age, sex, gender and race
come into play here.
02:58
You'll see those notations
on the actual lab work.
03:01
Now the GFR
less than or equal to 15 is a
medically defined as kidney failure.
03:08
That's pretty significant.
03:11
These are three numbers
you want to commit to memory
greater than or equal
to 60 considered normal.
03:18
If you're less than 60 could
indicate some kidney disease
but a GFR less than 15 is defined
medically as kidney failure.
03:28
Now when it comes to the GFR
being created with this fancy
math and the serum creatinine.
03:33
There's three things I
want you to keep in mind.
03:36
First of all,
the creatinine level
needs to be stable.
03:39
If the creatinine level is not stable
in this patient for some reason
the calculation will be off.
03:45
So we're expecting that creatine to
be at a fairly normal steady state.
03:50
So this test is not
accurate for patients
who have acute kidney
injury or dialysis
and last it's not
valid for patients
who are pediatric patients
or less than eighteen
years of age.
04:01
So when you see the
GFR of a patient
make sure their creatinine levels
have been relatively stable
that they're not in dialysis
and it won't help us
an acute kidney injury
and it's not valid for
pediatric patients.