Welcome to our video series on interpreting lab values.
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.
So let's give a quick review of what serum creatinine is.
It's a chemical waste product
and it's produced by muscle metabolism.
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.
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.
But serum creatinine can also help us estimate
how well the kidneys are filtering
right down to the glomeruli.
GFR is the glomerular filtration rate.
Now, that means how much blood is Passing through the glomeruli
for each minute.
So the serum creatinine helps us assess renal function.
It also helps us with the GFR.
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.
Now, you might wonder why we don't measure the GFR directly.
Let me help you understand a little bit.
The estimated GFR is this formula that uses
the patient's serum creatinine their age, their sex, and their race.
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.
We don't measure the GFR directly
because it's way too cumbersome to do that.
Now there are some special markers that are difficult to pronounce
and to spell not even going to go into those here.
Just take my word for it.
It's way too cumbersome to do that in a clinical setting.
That's why we use the serum creatinine
and the fancy math
to give us an estimate of how those glomeruli are functioning.
Now there's some unusual things about how a GFR is reported.
GFR greater than 60,
greater than or equal to 60 is considered normal.
Okay, so you probably won't even see a number
reported if your patients GFR is greater than or equal to 60.
When that glomerular filtration rate drops below 60.
That's when you'll start to see those numbers appear
on your patients lab work.
Now keep in mind differences between age, sex, gender and race
come into play here.
You'll see those notations on the actual lab work.
Now the GFR
less than or equal to 15 is a medically defined as kidney failure.
That's pretty significant.
These are three numbers
you want to commit to memory
greater than or equal to 60 considered normal.
If you're less than 60 could indicate some kidney disease
but a GFR less than 15 is defined medically as kidney failure.
Now when it comes to the GFR
being created with this fancy math and the serum creatinine.
There's three things I want you to keep in mind.
First of all,
the creatinine level needs to be stable.
If the creatinine level is not stable in this patient for some reason
the calculation will be off.
So we're expecting that creatine to be at a fairly normal steady state.
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.
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.