Anyone’s gfr from their labs differ from gfr calculators?

[FThomp]

My labs show a different gfr than what the calculators show. Is it bc there’s other blood related factors that get equated? Bc my creatinine has remained at 1.10 and bun 20 for over 10 years but over the years my blood labs show my gfr going from 96-70 in about 10 years. Note I didn’t get labs done every year though. But generally over that time they’ve remained at those numbers. According to the CKD-EPI creatinine equation mine is 94. Still not officially diagnosed but this is just my assumptions. I do understand muscle mass and different things like hydration and stuff can effect the test.

[Bet117]

Hi FThomp,

You are absolutely right hydration levels, time the samples were taken, changes in medication and or diet can effect your GFR.

If you are having the samples drawn from different labs, you may see a difference in the results as each has their own set of criteria and also how the blood, urine are spun.

GFR can vary from time to time and is based on hydration, blood creatinine level among other things. The tech spinning your labs may be looking at a chart by age to come to this conclusion.

My GP and nephrologist work out of two different practice groups and therefore results come from two different labs.

My nephrologist takes the time to calculate my GFR by hand, explaining how he comes to this conclusion.

Give the ordering physician a call and meet with him/ her regarding your concerns. You will get answers and feel much better.

Let me know how things go.

Bet

[RickHow]

I am not totally sure I follow what you are asking. But let's talk about it. I think you are saying that your Creatinine level has been constant at 1.10 for 10 years, but your egfr has gone from 96 down to 70. And you mention the results you get from labs does not match egfr calculators (I assume you mean you are trying calculators on the internet). Basically the results you get from online calculators and from labs should be EQUAL. Of course there are two exceptions. Recently the formula used by calculators has been changed. It used to report different results if you are Black, versus if you are not Black (there was no consideration given to other racial differences such as Asian, which makes no sense that they only reported Black versus non Black). The calculator has now been changed to eliminate race as consideration. Some labs have not yet implemented this change. BUT that would not be the reason your egfr dropped from 96 to 70.The other reason you can get different results from online Calculators versus the lab is what formula they are using. Most use the simple CKD-EPI equation (basically taking your age, creatinine level, sex and looking at a chart and reporting an egfr. NOT very exact. It is a one size fits all approach and does not consider factors such as your other health conditions, 1 vs 2 kidneys, medications being taken). Some labs use CKD-EP and takes into account Cystatin. Other labs use CKD-EPI and takes into account Crystatin C. Some labs use the MDRD equation).

All that said, to drop from 96 down to 70 is not likely due to these different formulas.

Sure hydration can change your egfr, because it changes your Creatinine level, but not 16 points difference!

10 years ago the 96 egfr may NOT have been with the CKD-EPI formula. This formual was developed around late 2009. This is 12 years ago. It was NOT immediately implemented by all labs until months later. Which would be around the time you were told you were level 96.

BUT none of that matters one bit. WHY? Because you say your Creatinine level has remained constant (1.10) for 10 years. THAT is what matters. It is therefore saying your kidney function is remaining the same. My doctors (of various specialties) all tell me to simply monitor my Creatinine level as the best indicator of kidney function.

[FThomp in reply to RickHow]

Well that’s a bit more of a relief to know bc I was so confused as to why my labs all looked the same but the gfr changed from lab to lab basically. I get that it fluctuates but it seemed a bit too much. Plus they never tested the cysts tin but I’ve heard the cyststatin + creatinine combined is more accurate than creatinine alone so I’ll try to get a cystatin test next time.

For those 10 years I’ve been a bodybuilder whos packed on about 250 pounds of mostly muscle with little body fat. I was on a high protein diet and creatine. I’m excited to see what changes happen since I recently lost 20 pounds, lowered my protein intake to normal levels, stopped all supplements, hydrating better and am working on lowering blood pressure as well. Thank you for your reply!

As of right now though, my gfr for my age according to the CKD-EPI creatinine equation (2021) is 94! I know gfr doesn’t matter as much as creatinine though like you said but it’s interesting nonetheless.

[RickHow in reply to FThomp]

You can pretty much count on the online calculators. There may be a difference of 2 to 4 points depending on if they use the race-based calculator or not. Yes, the Cryst is more accurate. But again, your Creatinine is constant. Also, there is a difference in your age (10 years) which usually accounts for a 3- or 5-point difference in your egfr (egfr goes down with age, slowly). By the way your BUN level of 20 is in the normal range. At the very top of normal.You did not give your age nor your sex. But if your report said your egfr was 70, and your Creatinine level was 1.10, you would have to be a 75-year-old male, or a 29-year-old female. If you are neither of these (approximately) go back to your doctor and find out how they determined an egfr of 70. The only other factor that could influence your egfr is if they did a calculation which used your exact height and weight, and you are taller/shorter, and/or heavier, than "normal".

[FThomp in reply to RickHow]

Thank you again for your reply. I’m 28 year old man six foot 2 230 pounds. I was about 250 when I had my tests done though and honestly all the calculators I use even factoring height and weight put my gfr in the 90’s however I do have high blood pressure I’m working on to get down and also frothy urine which may be protein in the urine but idk yet gotta talk to the doc! But the positive side is that my creatinine and bun have remained stable all these years so that’s a day of light for me. A silver lining if you will

[RickHow in reply to FThomp]

I tried some online calculators. If I have it correct you are a 28 year old male, six foot 2 inches, 230 pounds. Now most calculators do NOT ask your height and weight. They just use sex, age, Creatinine level. The up to date calculators do NOT any longer ask for race (they used to and a lot of them still do and are not using the latest formula which does NOT ask race). I get your egfr, using new calculators, is 94! I generally use the calculator from kidney.org. Now if you select the option where you can input your actual height and weight (which gives a much more accurate egfr), your egfr is 125!! You are perfectly healthy. The average egfr for a 30 year old male is 107. You do NOT NOT NOT have CKD or any problem.

About your frothy urine. There are literally over 100 posts on the forum on this subject. JUST having frothy urine is NOT an indication of kidney problems. You easily can have frothy urine, at any age from boyhood to elderly and the froth in urine is not CKD. Protein in the urine (a sign of kidney problems) IS an indicator of kidney problems. But you can have frothy urine for a million reason (I do, my father did all his life and died in his sleep at 92). This concern you seem to have can be easily checked and you don't even need a trip to the doctor if you don't want to. Go to the pharmacy and buy urine test strips. You urinate into a cup or bowl. Stick the strip in for 2 seconds, remove, wait 60 to 90 seconds and it will report if you have abnormal urine levels (it is normal to have some protein in urine, this will tell you if it is excessive). But I highly doubt you do. Highly doubt. Still bothers you, next trip to the doctor ask for a simple urine test (WHICH HE WILL USE THE SAME TEST STRIPS YOU CAN DO YOURSELF).

You are fine.

[FThomp in reply to RickHow]

Thank you!!! This puts me at ease! I’ve had high blood pressure for years and was scared it damaged my kidneys. This is good to know! I’m working on lowering it though and am on bp meds

[RickHow in reply to FThomp]

I too have high bp for long time. I take lisinopril 10mg and amlodipine 5mg daily and it keeps it well under control. After starting meds it takes at least a week or two to take effect. You are on the right track of weight loss, getting bp normal, exercising. Best of luck.

[FThomp in reply to RickHow]

Thank you, I appreciate your time. I’m hoping me and my doct can figure out a plant bc 25mg of losartan isn’t doing anything but we’ll see. I do know that losing some weight will always help. I was under the misconception being so Muscular was fine but weight is weight and muscle takes more out of your heart to supply and maintain from what I heard