Introduction to Glomerular Filtration Rate (GFR) Test (Nursing)

00:00 Hi! Welcome to our series on interpreting lab values.

00:04 And this one, I'm going to help you understand the glomerular filtration rate.

00:09 Now, you'll hear me say GFR from here on out because that is a mouthful to say.

00:16 Now let's start with the question, how many total liters of plasma do the kidneys filter per day? Don't look! Try and guess and see.

00:24 How many total liters of plasma do the kidneys filter per day? 180 liters of plasma per day.

00:33 Now, I am a huge diet Mountain Dew fan.

00:36 That is my beverage of choice.

00:38 But if you think of that what a two-liter bottle looks like in America, we all know what a two-liter bottle pop looks like.

00:45 That's 90 of those a day going through my kidneys.

00:49 That's pretty impressive.

00:51 So think about that as we're caring for our patients.

00:54 And as you're learning more about these kidneys they are amazing on what they do.

00:59 They are powerhouses.

01:02 Let's talk about the difference between GFR and eGFR.

01:06 Maybe you've seen that in your textbooks.

01:08 And don't you hate that when you don't know - like, is this the same thing, are these two different things? Well, technically they are two different things.

01:17 But let's talk about what the main difference is.

01:19 GFR is the glomerular filtration rate if we can actually absolutely measure it.

01:24 But eGFR with that little tiny E.

01:28 I want you just to underline that little E.

01:31 It's a calculation and that's why we put that Abacus up there to help you remember.

01:35 They're telling us the same type of information.

01:38 GFR is an actual measurement, eGFR is an estimate.

01:42 We use some fancy math to get that.

01:45 So let's talk about how this benefits and helps you understand what's going on in your patient's kidneys.

01:52 GFR is equal to the sum of the filtration rates in all of the, right, functioning nephrons.

02:00 Would you mind just underlining that for me? Okay. So this is of some of the filtration rates of all of the functioning nephrons.

02:10 As kidney disease progresses, those nephrons can be damaged.

02:14 They can be injured and they no longer function.

02:18 So keep in mind we're talking about the filtration rate of the functioning nephrons.

02:23 Now, it's really important because this is an assessment tool to kind of help us know and estimate the number of functioning nephrons in the kidney.

02:31 So you'll see GFR reported for most patients and especially those that were concerned about their kidneys.

02:40 Because GFR can help us identify the stage of the patient's kidney disease.

02:45 Now, we'll talk about that, but I don't want you to memorize it.

02:48 I just want you to know that it's arranged.

02:50 So why are we spending a whole video talking about GFR? Because this is something you'll use consistently in your actual practice.

03:01 So we want you to understand what it is.

03:03 We want you to know how we use it and we want you to see how we use it to grade kidney damage now.

03:09 Now, before we go on, we've talked about glomerulus in other videos, but I just want to remind you what that is.

03:15 Now look at the structure we have for you there.

03:17 See that little cup that it's set in? That's Bowman's capsule.

03:22 That holds that tangle of capillaries.

03:24 See those all knotted up in the middle? They're really not knotted up.

03:28 They just look tangled to us.

03:31 Those are the capillaries where we start to have the exchanges happen.

03:34 Remember capillaries are very thin-walled and the reason they're thin-walled is so that things can exchange back and forth across that membrane.

03:43 So they're also pretty fragile.

03:46 So that's why patients with super high blood pressure end up damaging their glomerulus.

03:51 We're not wired to take a hit.

03:54 Like a fire hose running through your kidneys.

03:57 That's why patients with chronic hypertension often have damage to their kidneys.

04:02 Okay. So this is the guy we're talking about.

04:04 This is the superhero of this video - the glomerulus.

04:07 When we're talking about GFR, we're talking about how efficiently that rate is happening right there in that little guy.

04:15 Okay. So this lab test requires a venous blood sample, and we prefer that or you could have some plasma.

04:22 So venous blood sample is pretty easy stick on most patients.

04:27 We need that sample and what color tube do you think we put it in? Well, we always tell you here at Lecturio, that when you have that in mind when you're drawing lab work, that we use a gel barrier tube.

04:38 So it could be a red-top tube, a green-top, which is heparin tube, or a lavander-top tube, which is actually one of my favorite colors, but I digress not something you need to know for lab work.