Welcome back. Today on the PKD Dietitian Podcast, we have another listener question episode. I'm Diana Bruen, your host creator and the one and only PKD dietitian, and without further ado, let's jump right in. Tania wrote in with the question what is the difference between EGFR and GFR? Is one better than the other for testing with PKD, or should I ask for both? I am worried I am not getting the labs. I need to stay informed about my kidneys. I get questions around this topic more often than you can imagine. It is confusing for many folks out there Learning what labs measure or even mean out there Learning what labs measure or even mean what the abbreviation stands for, let alone what results show. It's like learning a new language. So before we dive into the differences between EGFR and GFR, I want to make sure all the listeners tuning in know what those abbreviations stand for. Gfr stands for glomerular filtration rate and EGFR stands for estimated glomerular filtration rate. You are going to find one or the other listed on your kidney function lab results. Now the question is what do those lab results show? Before we get to that, I want to back it up a little bit and take a little peek inside the kidneys.
Your kidneys, as you know, filter blood by removing waste and extra water. In doing that, they make urine In your kidneys. You've got lots of these tubules and at the very top of the tubulars there are these tiny little filters. If you can imagine, it almost looks like a little knot. Those are the glomerulus and those are your main kidney filters. So you can see where that word comes from in the abbreviation glomerular filtration rate. Now, of course, it is a bit more complicated than this, because your kidneys are badass and they do lots of stuff for your body, but you get the big picture. You've got these tubules and these filters and when we're looking at glomerular filtration rate, we're really looking at how well those filters are doing, because glomerular filtration rate can't actually be directly measured. What we look at instead is what is left over after your kidneys do their filtering job. We're looking at what ends up either at higher or lower levels in your blood and sometimes in your urine, because we know what quote-unquote normal ranges are for these tests. In general, a higher GFR means that more filtering is going on, and a lower GFR means less filtering is going on. When there's less filtering, this is when waste can build up in your blood and shows up on your labs as higher than what's considered a normal range.
There are several ways to look at your kidney function and get an idea about what's going on. This is where both GFR and EGFR come into play. Technically, they aren't the same thing. So let's talk a little bit about EGFR, your estimated glomerular filtration rate. This is the test you get with your kidney panel and regular blood work labs that are drawn by your nephrologist or your PCP and, as you know by now, they draw blood and they get your creatinine levels and they also give you the EGFR. Creatinine is the waste that they are looking at, the waste they're looking to see. Is it higher, is it normal, is it lower? They take your creatinine amount and they plug it into an equation. Now this equation also takes into consideration things like your age, your sex and other factors. Plugging your creatinine into that equation. It calculates what your estimated function is. Your lab results give you a snapshot of what your function is at that time. Here are the benefits of why we use EGFR because it's quick and it's widely available, it's generally affordable and it's standardized. We've got a standard equation and a standardized process.
If you want to see this process in action. Here is what you should do. The National Kidney Foundation has a great online EGFR calculator. I've linked it out in the show notes. Go to the website and plug in your details and your latest lab result for creatinine. Hit calculate and scroll down to see what your estimated GFR is. Now you'll see a spot for cystatin C. You can leave that blank. That's another waste that can be measured and used to estimate your kidney function. If you're curious to learn more about Cystatin C, check out episode 33. I've also linked that out in the show notes. So now let's switch over to GFR, which is sometimes written as MGFR, and what this means is it's measured, and what this means is it's measured.
Getting a measured GFR is a lengthy and complicated test process, one that is often only used in studies and research. It's very rarely done on an individual basis. A measured GFR measures how quickly your kidneys filter a particular substance. Because of that, it is a timed process, and the substance that is used is ones that our bodies don't naturally produce. So here's how it works. In general, a test participant who is in the study will get injected with something that our bodies don't naturally produce. At specific time intervals, they measure how much has been cleared and this gives an accurate measure of kidney function. It is more precise but it's also much more involved. I can guarantee that the majority of you listening have not had a measured GFR done. It's complicated, costly, time-consuming and really not commonly done.
Back to Tania's question Are eGFR and GFR the same? Although both look at kidney function, they aren't technically the same thing. So hopefully now you have a better understanding of what each test measures. One is an estimate, one is a measure, and how they do it. But know this the results that you are getting back from your blood lab are all an estimated GFR, an eGFR. Often your lab results don't spell out that it's eGFR. You might see it written as GFR. Unfortunately these two are used interchangeably sometimes. Can you see how it all gets confusing? Technically eGFR is the correct scientific abbreviation, but that isn't always what is written, said or documented in labs or research.
Now to the second part of Tania's question do I need to get both tested with PKD? And the answer is no, you do not need to get them both tested. An estimated GFR is absolutely sufficient for monitoring and looking at your kidney function and trends. However, with PKD, if you really want to look at what's going on with your kidneys and in your kidneys. Getting an MRI and total kidney volume is the golden standard. Thanks again to Nia for taking the time to submit your great question.
If any of you out there my listeners have a question about kidney health or PKD or nutrition for PKD, feel free to send it my way and I'll do my best to answer it in a future episode. If you're curious about learning more about your labs, what they mean, what they show and things outside your kidneys that can affect your results, check out Master your Labs for PKD. I love this course. It is self-paced. You get to go in and pick which lab you want to look at and learn more about. I have linked it out in the show notes for you. You can automatically sign up and you can even learn more. It's a powerful resource for the PKD community. And that's all for today, folks. Thanks again for tuning in and I'll catch you on the next episode of the PKD Dietitian Podcast.
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