GFR appears to be an actual measurement of the rate at which your kidneys can filter your blood.
eGFR seems to be an inferred version of the above. It centres on your creatinine readings: that number being fed into an equation, the GFR then being an estimated number.
But creatinine can be lowered by going on a protein restricted diet. So if you go on such a diet and your creatinine lowers, you would expect your eGFR to increase. But this doesn't mean your kidney can filter at a higher rate. It just means you are throwing less work at them, them filtering at the same rate as before, probably.
I suppose that in order to find out the actual health of your kidneys and the rate of progression of the disease, you'd have to have the actual GFR calculated.
Is this correct?
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Skeptix
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eGFR is not inferred, it is an estimated GFR. If you look at your paragraph starting with "But creatinine..." you'll need to realize that is the whole key to slowing the progression of CKD. Your kidneys do not regenerate. Once damaged, they are beyond saving. All you can do is slow the progression and save as much of the function as possible. Now there are some temporary situations where mild damage has been done and the cause may be a certain medication (only one example) and by stopping it in time some kidney function may be returned. Simply put, that is how your kidney function can increase. I was diagnosed at 32 but have had it as high on 65 and over all the time since my diagnosis I have managed to average 50. Following sound, competent medical advice, adhering to a kidney-friendly meal plan designed for you, following a medically approved exercise regimen, and keeping any underlying conditions under control, whenever possible will be the key to slowing the progression and preserving your remaining kidney function.
I've included an article for you that simple explains the difference between GFR and eGFR.
I suppose I meant that we were inferring what the actual GFR was by another (easier to apply in practice) means. Just as we infer (or estimate) that it must be nighttime outside (if we cannot see outside) by looking at the amps being drawn by the city's lighting circuitry.
I read your link, thanks. It doesn't really say what GFR is - but I am supposing I'm right in thinking that its an ACTUAL measure of glomerular filtration (like filling a measuring jug from the tap tells you the ACTUAL flow of water from the tape).
So I understand how eGFR can increase (by, for example, going on a low protein diet) whilst GFR (if it were being measured) keeps declining. I was supposing that it would be better to know the actual rate of decline (GFR) than knowing the inferred or estimated rate of decline (eGFR). The only way to know whether you are optimizing your management is to measure the actual rate of decline (I would have thought).
As for your kidney not actually being able to improve (in real terms). Say they are inflamed? Their function will be reduced (say the blood vessels are swollen by inflammation and so narrowed and so less able to filter the same quantity of blood). But if you eliminate the inflammation, then surely you improve the performance of your kidneys?
Dunno about the medics. I'd have to find one up to speed. Someone on here pointed to the idea of finding a dietician online (since they are really only dialysis focused in Ireland). Found kidneyRD.com but they are pushing a ketoacid full of calcium. I know someone has to earn a buck, but you have to be suspicicious of laying your life in someone elses hands.
Thanks. Whilst appreciating eGFR as of some use, there is the issue mentioned in the OP. From your link:
"The eGFR is a good test, but it’s not right for everyone. For example, this test may not be accurate if you are younger than 18, pregnant, very overweight or very muscular..."
... or you go on a very low protein diet and as a result, your creatinine numbers improve dramtically. And because they improve, so does your eGFR.
But you kidney function is still declining, despite increasing eGFR and we don't know what that rate of decline is.
If you want to play word games this isn't the forum. In the article I posted it states very clearly what GFR stands for and what it means. There is a very specific test for GFR but the norm is the eGFR which appears on most lab reports. You can request the GFR test but it won't change drastically. The eGFR test is one of several tests to determine where you are in CKD. It goes along with sCR, BUN, and ACR. The eGFR average gives you a more reliable, over time, of your kidneys ability to function. The GFR or the eGFR test is not the sole indicator of CKD.I provided you with one example of medication that may call up a lower eGFR number and that may be able to change without permanent damage as long as there was no severe damage done to the kidney(s). There are, as I mentioned, other reasons for the low number of one test. That is why when someone diagnosed with CKD has a low eGFR they may be able to raise it by the meal plan, exercise, and controlling underlying conditions.
I'm not playing word games. Nor am I saying that eGFR hasn't a general diagnostic use. I'm looking at the use in a specific situation.
That article says what GFR is "glomerular filtration rate", but doesn't say what that means. Expanding on an acrynom doesn't say very much.
Much is said about eGFR however.
Let's take me: someone who has been told they have CKD but not to worry about it. I'm munching away happily on protein galore. What is it, 1.2g/kg/day? My eGFR is 35 because my damaged kidneys can't process all this excess protein.
Then I go on a vlpd + keto. I eat protein at levels my kidneys can process. My creatinine goes down - heck it might even come into normal range.
Would my eGFR change "drastically"? Well yes it would, seeing its based on creatinine. Would my GFR change? Probably not. Indeed it might get worse.
If you accept that eGFR can improve (e.g. were one to switch to a low protein diet) whilst GFR can disimprove (since CKD is progressive) then you'll see my point.
"... My eGFR is 35 because my damaged kidneys can't process all this excess protein."
It's more complex than that. While there is creatine found in food like read meat and fish not all protein contain creatine. Your body can synthetize creatine to meet its need. The fact that it use ammino acid to do so may or may not be relevant (beware of simple conclusions). umich.edu/~medfit/supplemen...
While it's not covered by this article, creatine level can also vary based on the amount of physical activity, muscle mass and others. But I lack proper knowledge to make conclusion. Since the guidelines point to a fairly low amount of protein I am going in that direction (not necessarily vlpd which appear to have enough pluses to be mentioned in the nkf guidance) and so far I am feeling better. Oddly enough my creatinine level have increased but my BUN is now back within normal range. But I leave the interpretation of those numbers to the specialist. I am glad that I know that the amount of physical activity can affect creatinine level and I will likely bring it up and discuss with them to know whether or not I should be worried.
A good example of something that I wouldn't do to improve those numbers would be malnutrition. It may look ridiculous yet it is something that I may have underestimated along with PEW (Protein Energy Wastage I believe). One more thing to discuss with the specialist, not something to panic and go in random direction. I know myself.
Creatine/Creatinine. You seem to be speaking of creatine whereas I'm speaking of creatinine?
The latter appears to be waste product, with serum levels being heavily influenced by the amount of protein we eat. Given serum levels are used in arriving at eGFR (and eGFR being used as an indication of the health of our kidneys) one wonders as to it's use.
Can you see my point: we can have a situation where eGFR is "improving" whilst actual GFR is disimproving. Wouldn't one want to have an idea of the true picture rather than an estimate which might be telling you the wrong thing?
As for vlpd? Not only mentioned in the NKF guidance but the NKF point to vlpd + keto is better than a lpd. Given the amount of protein in meat, it seems to be impossible to keep on consuming it on a vlpd+keto diet. Thus vegan vlpd+keto the conclusion.
At the moment, only urea and creatinine are out of spec in my bloods. It makes sense to me to diet to get these as near back into spec as possible given excess toxins floating around progress the disease.
"Can you see my point: we can have a situation where eGFR is "improving" whilst actual GFR is disimproving."
Yes, absolutely! Does it mean that the eGFR is useless? I believe that you have many reply showing the opposite, one of many metric used to monitor kidney health. Yes I do believe that there is an element of risk where it could be misinterpreted but that in itself doesn't make eGFR useless.
"Creatine/Creatinine. You seem to be speaking of creatine whereas I'm speaking of creatinine? The latter appears to be waste product, with serum levels being heavily influenced by the amount of protein we eat."
AFAIK the simplified relationship between creatine and creatinine is that creatine is used to generate ATP energy. 1 of 3 energy system, ATP releasing energy almost instantly and depleting extremely fast (think 100m sprint or olympic weightlifting). Your body can synthetize its own creatine and some food can also provide creatine. It can also be supplemented and most but not all people will see an improve of performance (personally I tried and I found it to be negligible). It is my understanding too that creatinine is a waste product although it doesn't mean that it doesn't serve any other purposes. It likely does and may not be fully understood or it might be suspected to be. I don't think this is much relevant when it comes to kidney health, however. At least not to this discussion.
That in itself have nothing to do with protein intake. Saying that it is influenced by protein intake seem to hold some truth in case of CKD. But heavily? I am not so sure. It might be one of the few things that we can control and improve but that doesn't mean that it will be heavily influenced. What about fiber intake, electrolytes balance and exercise to name a few? Yes exercising in itself could generate more creatinine and not all its risks and benefits are fully understood yet it is recommended and appear to be a net beneficial.
You could read more about creatine here. This research in itself doesn't appear to be relevant to CKD but the first 3 paragraph appear to provide a good picture of creatine. Also pay attention on how there are still unknown (at the time this research paper was written) such as "The mechanism of creatine absorption in thegastrointestinal tract is unclear". AFAIK it is very much the case with many aspects of CKD, there are lots of unknown. They might not know why taking action X produce a positive outcome for example.
But frankly you'd be better served by reading about the science itself at the introductory level about those topics. It won't go as deep but it will give you a better foundation. It will take more hours and efforts but if you have an interest in this area it will be more than worth it. I can't recommend a book about human metabolism because I have never read any but this book about science of nutrition may serve as a nice introduction. It also happen to have reference to books about human metabolism. It can be purchased for less on amazon but the publisher website have a nice interface to search for a book that might suit you better. Or use google to find the list of books required for completion of course XYZ and start from there.
I just want to double-confirm there being no intent to get into argument here. There's a fair chance I'm bringing a lot of frustration with me - I started out with a GFR of mid-50's on original diagnosis and have had absolutely near enough zero by way of advice /warning as to the need to manage this disease.
So when eGFR is held up as some kind of measure which may very well not be a useful-to-me measure, I get a bit irked.
No intent to offend Mr Kidney or anyone else. Apols in the event I did
There is some discussion in professional circles that splitting off eGFR for African Americans is inappropriate. If you are white, the eGFR for non-African Americans is the number to look at. The eGFR number is the standard for a quicker determination of kidney function. There is another more involved test for GFR that will produce a slightly different number. However, most physicians don't order that test unless unexplained and unexpected results are in play.Once you have a diagnosis of CKD start averaging your eGFR for a more realistic idea of your kidney function.
The diagnosis of CKD is only made after several sets of labs and include a number of individual blood and urine tests to be conclusive.
Accept the findings and follow the advice of your Care Team. Change a doctor if you aren't given the respect you are entitled.
I don't want to get into the word play argument but Mr_Kidney has a point. I don't think there is a single metric out there that doesn't have its limitation. To me it appear that you are trying to take simple conclusion out of a nuanced answer. That simple conclusion does not exist and I've seen GP doing the same mistake at times.
If I am not mistaken you have said that you are a mechanical engineer? In a way it's not much different than trying to take a measurement inside complex mechanism, where the most direct measurement is not possible and would interfere with the system and create a false reading, or physically impossible. Or how different types of imaging (such as x-rays) or eddy-current have their limitation and AFAIK they must be interpreted.
AFAIK you can't directly measure the amount of potassium present in a cell. Or know whether or not you are getting enough calcium by measuring the level of blood calcium as it is tightly regulated and would remove calcium from your bones. There are likely messengers or indirect way to determine this but I hope that you see my point, it's not an absolute measurement.
If anything it reinforce the need for specialist to interpret those numbers and how crucial the guidance such as those from the NKF are.
Would I take approach XYZ solely base on eGFR or GFR numbers? Absolutely not. I'd be more interested whether that approach produce a better outcome, slow down the progression of the disease, improve quality of life or something else. And while these are not absolute metrics (edit: eGfr) likely hint in that direction. It's also where it can get very tricky to interpret those results as those number may show an improvement and still be called statistically insignificant. Or assume that all will be well because study on rats went well. A bodybuilder named Bostin Loyd recently went through a kidney failure after taking a substance that was never tested on human before and for which there were no dosage available, the video is named "Bostin Loyd: The TRUTH About My Kidney Failure" (I din't want the preview to be visible - not a channel that I regularly watch but it caught my attention). It's a bit on the extreme but it is certainly possible to get more harm than good based on a fake, flawed or misinterpreted study or statistics.
Interpreting those statistics is something I don't properly understand, another area where it's quite easy to take simple conclusions out of a nuanced answer. It's something that you could understand better by studying the science directly. I am not certain which exact field you should read or take courses but if you put enough effort into it I believe that you can succeed. It will likely be harder than you expect but certainly feasible.
I absolutely agree with your approach - there are any number of factors to consider to get an overall picture and it is my intention (indeed, I am in the process of) getting to mechanical grips with how this disease is to be managed.
Part of that coming to understanding (which has only recently started) is querying things, interrogating things. And eGFR appears to be one of those things in which great store is put.
Whereas my (embryonic) understanding realises that it's a measurement of something that is seriously affected by the amount of protein you happen to have eaten. I understand metrics have their limitations but it seems to me that eGFR (as applied to me thus far) is for the birds. No account is take of the amount of protein that I've been consuming.
Now, if I regularise my protein intake so that it is same (or near enough) every day, then my creatinine reading becomes a useful indicator as to stability of kidney performance.
"Now, if I regularise my protein intake so that it is same (or near enough) every day, then my creatinine reading becomes a useful indicator as to stability of kidney performance."
It is something that you should discuss with your health professional and I think that you should be careful when making conclusions that appear to be set in stone. I hope that by now you understand that creatinine is not a byproduct of protein and is not generated as protein is broken down.
There are as many way to interpret those results as your imagination permit and not all of them will be valid, some might hold true by pure coincidence. I'd be lying if I was saying that I don't make my own understanding out of it but I do know that my knowledge is limited and could leave me overconfident or worried when I shouldn't. l leave the conclusion to the specialists but if nothing in my life routine have changed and my number fluctuate I might be worried. If my GFR slightly dropped or stay the same while the amount of exercises increased I might not worry but maybe I should. All I can do is to make sure to mention those (potential) factors to the specialist and listen to what they are going to tell me. They could tell me that the fluctuation is normal or perhaps there are no conclusions possible out of those factors. That's why it's important to have a medical team that you can trust.
"That's why it's important to have a medical team that you can trust."
Therein the rub: I don't have confidence in my nephrologist and the idea that a(n average Irish) GP would be someone who'd understand my figures better than an informed self, is nigh on laughable. It's not the set up here.
Which is not to say I oughtn't look around. My GP isn't bad generally (compared to typical 10 minute revolving door practices) and it might be that when I next approach, armed with info and intent to take control she'll ramp up her interest. But I've a sinking feeling that the relatively small pool of nephrologists in Ireland won't be much other than what I've already experienced. The Irish tend to be tyre kickers on matters progressive. I fully suspect that mention of a vlpd + keto diet will result in a furrowed brow and quizzical expression
Got it on creatinine not=protein intake (I was reading from Wiki which had protein consumption as an influencer). Suppose I'll focus on the urea side of things when I've racked up a month or three on this sweet child (somewhat tasteless, hard to rack up the calories) vlpd+keto diet o' mine.
I wouldn't necessarily focus on Urea because of that, something to discuss with your specialists. It's also possible that you are doing everything right and as a result slow down or halt the progression of your CKD and your bloodwork may not improve because of that.
Finding the right specialist can be quite daunting and to be honest I don't really know how best to choose them. One thing I would suggest is to look at their curriculum. They likely all have different strength and weakness and none of the will be perfect. One might have the absolute perfect knowledge and expertise if you were to be on dialysis but not be tooled to serve your right now. One might be specialized in electrolytes imbalances but maybe you don't have those issues.
At some point you can't expect a specialist taking care of patients to know and master everything like a full-time researcher would. Perhaps in an ideal world looking for one that just happen to take care of patients and performing research that are relevant to your case would be ideal but there are only so many specialists and research being performed out there. And yet that theoretical ideal specialist might not be able to answer all of your questions.
Don't get me wrong, looking to fine-tune your nutrition with bloodwork absolutely make sense but could be much harder to implement and achieve a certain level of perfections than it might look. For example Bulgarian weightlifter had literally bloodwork done after their workout to determine exactly how much of this or that vitamin/mineral they needed. And all the dedicated team they had in the background for analysis. Without state sponsorship it might be impossible to achieve. But there are also medical transdermal sensors (azosensors.com/article.aspx... that are becoming somewhat more mainstream and I have not look deeply into it. It may only be a matter of time until one is developed specifically for CKD patients or it might already exist. I see many pluses compared to constantly getting yourself poked too often which may do more harm than good.
I am still working on the basics and they do cost money so I will be looking at those later, some more than I have currently available. For me it's a dilemma, there are lots of different approach that I could take but the amount of money I have is limited. For example, should I save some money for steam cell treatments or (edit: something else or) spend it on a vlpd diet? I know that you opted for the latter and I respect your choice. I might be able to afford more of them in the future but not right now.
To answer your original question, yes, you are generally correct in your understanding of measured GFR vs. EGFR, but the subject is a lot more complicated than can be expounded upon here. I think you might find this interesting;acutecaretesting.org/en/art...
From what little I've read from you, I suspect you're gonna be a pro in no time flat. Keep up the research and continue to be skeptical. You'll thank yourself. And btw, anybody who's a fan of The Far Side deserves respect right from the get-go.
I have hereditary kidney disease, diagnosed in infancy. My sister is a skeptic like you. She had an actual GFR done during a study of our familial disease and it was quite different than her eGFR. It showed her kidneys were performing better than they thought. She was not . and is not on a restricted diet because her disease is very mild. I have had a GFR done only while hospitalized 50 years ago. Since then I've had to rely on these estimated numbers. Not confidence inspiring on such an important metric. I decided to put off dialysis, no matter what the eGFR until I felt ill. I had none of the outward symptoms until my eGFR sank to 7 for successive labs. Finally, my energy just gave out and I had increasing edema. So, now I'm on PD since the end of March. Maybe it's too soon to tell, but I don't see much difference except that the edema is gone.
I just look at my electrolytes and minerals...phosphorus... calcium...potassium..etc...to see how clean...or not clean.....my blood is...and adjust what I am doing
Blood Pressure....temp...and weight...an increase in weight can indicate fluid retention...check for swelling..especially in ankles and hands...I am on Home Dialysis and I am to check Vitals twice a day...Phosphorus and Potasium are the main ones I watch....but I look at all that my Dr. orders...I keep all my labs and I just try to watch the trends...
Admire your keen interest in figuring things out. I really don't have anything to add to this thread other than the fact that as my husband's kidneys started their downward spiral, his creatinine levels became of intense interest by his nephrologists. Anything to do with gfr was a mere footnote - creatinine was the focus (and blood pressure) for most all decision making which, in hubby's case, led to dialysis. Keep on seeking answers until you're satisfied; knowledge is power.
That's the hope: to find a way of wresting control from others. Call it control freakery. Call it skepticsm.
I can only observe from the rest of my life's experience which notes that most people aren't particularly good at what they do. Okay maybe a fair few of them, but really top drawer? That's rarefied atmosphere territory.
So why any different a doctor? I know in my country, the reason folks go to med school isn't necessarily that they always wanted to be doctors.
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Gfr improvement.
Creatinine vs. CystatinC eGFR
Why are eGFR calculations different?
Am i truelly in stage 3a ckd. 
GFR dropping fast!
