1/10 We often talk about evaluation of AKI in the context of ⬆️ creatinine, but let’s take a step back and think about eGFRs. Here is an approach to interpreting ⬇️ in eGFR! #NephTwitter #MedTwitter #FOAMed #MedEd
2/ This differential focuses on the estimated GFR (eGFR), which is calculated using serum creatinine +/- serum cystatin C levels (we will take a look at the equations in a bit). Biomarkers that actually measure GFR (such as inulin) are not clinically practical to obtain.
3/ Thanks to @ZacNephron for explaining GFR vs eGFR, referring me to Chapter 2 of @BookBurton, and sharing this thread to deepen my understanding of the utility of GFR:
4/ Not all ⬇️ in GFR are bad! After posing about a question related to this, @NephroMD and @VelezNephHepato reminded me that some drugs transiently ⬇️ GFR but actually preserve GFR in the long-term (reminder that we will see Cr ⬆️ with these medications).
5/ In order to break down this approach, we need to look at the calculations that go into estimating GFR. @NKF has the CKD-EPI Creatinine Equation (2021) and the CKD-EPI Creatinine-Cystatin Equation (2021). Make sure to pay attention to which equation your institution uses!
6/ If your institution still uses an eGFR calculator that uses race as a variable, this is a good opportunity to advocate to change that. Thanks to @MichaelAyoubMD for sharing this thread by @kidney_boy
7/ Using the above equations, we can look at the factors that cause a ⬇️in eGFR:
⬆️ age
⬆️ creatinine
⬆️ cystatin C
⬆️ age
⬆️ creatinine
⬆️ cystatin C
8/ Here is a non-exhaustive list of causes of ⬆️ creatinine. The medications listed that ⬇️ renal tubular secretion of creatinine are from a question that I posed:
9/ Here is a non-exhaustive list of causes of ⬆️ cystatin C
10/10 Here is a summary slide. Would love to #askenal for any feedback! Thanks to @ZacNephron, @MichaelAyoubMD and @DxRxEdu for reviewing this thread. And for those using Glass.Health, here is the shared link to my schema on reduced eGFR: glass.health
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