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So how do we evaluate the renal function in the aging? Well here's 2 tests I want you to
keep an eye on. The 2 tests that we can use are an estimated GFR and we can do that
with some fancy math that you don't have to do, lab does it for us. And we can look at
creatinine clearance. So I'm going to break both of these tests down because it's
important that you understand what they tell us about the kidneys. Now, suddenly
renal changes start after age 30 so it does kind of kick in relatively earlier than you
would think it would. The GFR is the glomerular filtration rate. When you see that
little e by it, that's an estimate of how much blood is actually passing through that
glomeruli. Those little tiny filtering units in the nephrons each minute. That's what GFR
is and then we can have a pretty wide range of variability among individuals. Okay,
so when you're talking about age-related changes or decreases in GFR, there can be
a wide range that's still considered normal. But remember these changes start at the
age of 30. So, a rough estimate for you, something to kind of keep in mind is there is a
decline in their estimated GFR of up to 10% per decade. That's just kind of a rough rule
of thumb. Now you also are going to have impaired electrolyte and water management
because that's what the kidneys do. Right? That's one of the things that kidneys do is
they manage electrolytes and our fluids on-board. So, as you have a change in the eGFR,
the function of the kidney, you're going to have, relative to what they were, impaired
electrolyte and water management. So let's look at eGFR across the lifespan.
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So we're taking with our little fellar again when Jose was a little tiny guy, you have a
low GFR at birth. Seems kind of weird but remember everything is immature in babies.
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Right? They're just brand new to the world. So their lungs are immature, their kidneys
are immature, their lungs are immature. It's okay. It's normal to have a lower GFR.
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Now by the age of 2, the terrible 2's, you'll be just right around an adult GFR level.
02:21
Let's look at up to age 40. The GFR maintains usually around 140 ml a minute and then
you got that really ugly 1.73 m2. Don't worry about that. We usually just speak in that
number, but we wanted to make sure we included the units for you there. So, GFR levels up
to about age 40 should be around 140 ml. The second of the two tests that we're talking
about evaluating renal function is creatinine clearance. Now creatinine clearance can
decline by 0.75 ml per minute per year in older adults even if they don't have kidney
disease or other comorbidities. Now, comorbidities refers to other disease processes,
maybe like hypertension, diabetes, any of those other comorbid conditions. So, most
important point: creatinine clearance can decline by this amount, 0.75 ml/min/year
in older adults even if they have no other current disease processes. Now, on the cool
side, not all older adults experience this decline. Okay, so it doesn't have to happen
but it's still considered normal if it does. Now, independent, so separate from the
creatinine clearance, kidney physiology is going to change with aging. Remember we
talked about structure and function and hormones. That's going to happen, but even
independent of the creatinine clearance test we're going to see those changes.