Thread by @kidney_boy

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