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Joel M. Topf, MD FACP

8 Dec, 11 tweets, 4 min read

I am going to try to recap my recent grand rounds on race and GFR in a few #tweetorials. Here is the second one. You can find the presentation files and a video of me presenting at pbfluids.com/2021/12/the-ne…… 1/10

To understand how nephrology got itself into this eGFR and race mess I want to unpack what is going on in the equations. What are they trying to do and how do they work. 2/10

Estimated GFR depends on people being in steady state. Steady state means the Day 1 creatinine = Day 2 creatinine = Day X creatinine. It doesn't matter if the cr is 0.6 or 4.4, as long as the cr is roughly the same from day to day they are in steady state. 3/10

And if the creatinine is stable from day to day that means creatinine in = creatinine out. 4/10

So we can set the determinants of Cr in equal to determinants of Cr out. Renal excretion is broken down into serum Cr x GFR + Tubular secretion. so the final formula looks like... 5/10

...the equation! And then we will use some simple algebra to solve for GFR 6/10

GFR equals a whole bunch of variables divided by serum creatinine. That "bunch of variables" are the non-creatinine determinants of GFR. Those non-creatinine determinants of GFR mean that the same Cr can represent a wide range of GFRs in different people 7/10

In order to operationalize this we use measurements and demographic variables to try to estimate these largely unmeasurable non creatinine determinants of GFR. These are the GFR estimating formulas. The oldest is Cockcroft-Gault, the most referenced nephrology paper ever! 8/10

Cockcroft Gault is a simple formula
CrCl = (140-age) x wt / (Cr *72)

But it doesn't even estimate GFR, it estimates CrCl. **It is an estimate of an estimate**

Also there were almost no women in the study. They just guessed on the 0.85 factor for women🤯 9/10

Despite these glaring problems with Cockcroft Gault it became the coin of the land until Andrew Levey rode in with the MDRD equation (next Tweetorial)...10/10

Forgot to attach this picture to that last tweet 10b/10

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More from @kidney_boy

Joel M. Topf, MD FACP

@kidney_boy

10 Dec

I am going to try to recap my recent grand rounds on race and GFR in a few #tweetorials. Here is the fifth one. You can find the presentation files and a video of me presenting at pbfluids.com/2021/12/the-ne…………… 1/10

Use of race in eGFR is doesn't work because race is a social construct. “A person who could be categorized as black in the United States might be considered white in Brazil or colored in South Africa” Racial identity shifts with experience and time. 2/10 nytimes.com/roomfordebate/…

I spoke Danish at home. I ate Danish food. At Christmas we danced around the Christmas tree singing Danish carols. But when I went outside my home, I was black. nytimes.com/roomfordebate/… 3/10

Read 11 tweets

Joel M. Topf, MD FACP

@kidney_boy

9 Dec

I am going to try to recap my recent grand rounds on race and GFR in a few #tweetorials. Here is the fourth one. You can find the presentation files and a video of me presenting at pbfluids.com/2021/12/the-ne………… 1/10

So both MDRD and CKD-EPI found that Black Americans had a higher GFR (on average) for the same creatinine compared to White Americans. Also NHANES showed that Black people have higher creatinines than White people. Why? ajkd.org/article/S0272-… 2/10

Looking at non-creatinine determinants of GFR there are a limited number of variables. Though I included "metabolism" that only comes in play at high serum creatinine so that can't be the factor here.

Increased production from increased muscle mass was the prime suspect. 3/10

Read 11 tweets

Joel M. Topf, MD FACP

@kidney_boy

9 Dec

I am going to try to recap my recent grand rounds on race and GFR in a few #tweetorials. Here is the third one. You can find the presentation files and a video of me presenting at pbfluids.com/2021/12/the-ne……… 1/10

In the 1980's the hot idea in nephrology was low protein diets to preserve GFR. The NIH funded a Big Science study to test the theory, the Modification of Diet in Renal Disease study, MDRD. The study was a mess and fell on its face, but they did collect a lot of cool data! 2/10

Among that data was iothalamate clearances which are a really good approximation of GFR. So Andy Levey and friends took those data and combined it with age, gender, and race to come up with the MDRD formula. 3/10

Read 10 tweets

Joel M. Topf, MD FACP

@kidney_boy

8 Dec

I am going to try to recap my recent grand rounds on race and GFR in a few #tweetorials. Here is the first one. You can find the presentation files and a video of me presenting at pbfluids.com/2021/12/the-ne… 1/10

My parents grew up in the segregated south and tell me stories of toe curling segregation. They are embarrassed to say that at the time, it seemed normal. 2/10

What are we doing today that we will look back at as being unconscionably racist?

I think we will look at the two separate GFRs listed on a routine BMP like the two drinking fountains. 3/10

Read 10 tweets

Joel M. Topf, MD FACP

@kidney_boy

2 Dec

More fellows find NephJC to be “very effective” than:
CJASN, NephSAP, JASN, textbooks, KDIGO, AJKD, journals, RFN, and more. Wow. Just wow. asn.apprisor.org/epsAbstractASN…