How to Avoid Freaking Out About Kidney Function

This transcript has been edited for clarity. 

Matthew F. Watto, MD: Welcome back to The Curbsiders. I’m Dr Matthew Frank Watto, here with my great friend and America’s primary care physician, Dr Paul Nelson Williams. 

We had a great discussion with Kidney Boy, Dr Joel Topf, everyone’s favorite nephrologist, and he taught us how to manage blood pressure in chronic kidney disease (CKD).

When should I start freaking out about a patient’s kidney function? 

Paul N. Williams, MD: Dr Topf focuses more on albuminuria than we are used to doing. It’s probably one of the most important prognostic indicators of how a patient is going to do from a renal standpoint.

Historically, I’ve tended to focus on the estimated glomerular filtration rate (eGFR), and the lower that number gets, the more I sweat, but albuminuria is probably equally, if not more, important as a way of prognosticating whether a patient is going to progress to dialysis or transplant. He directed us towards this nifty little calculator, kidneyfailurerisk.com, where you plug in the patient’s age, eGFR, and degree of albuminuria, and it spits out their risk of progressing to hemodialysis or renal transplantation over the next 5 years. It’s a nice way to concretely explain to patients their risk for progression.

Instead of telling the patient, “You are high risk,” Dr Topf will say, “Your risk is 6% of needing dialysis in the next 5 years.” You can even use these thresholds to gauge when to refer a patient. If someone has a 5-year risk between 3% and 5% or higher, that patient should probably be seeing a nephrologist.

If their 2-year risk is greater than 20%, that patient probably should be evaluated for transplantation. This gives us have more concrete numbers to work with rather than just saying, “Your kidneys aren’t working as well as we would like and you should see a kidney doctor.” Patients have a better sense of how serious things might be. 

Watto: It’s just easier for them to understand. Dr Topf made the point that we used to have a heat map based on the stage of CKD that would tell you how high a patient’s risk was compared with other people. But patients don’t really understand relative risk, so Dr Topf tells them their absolute risk for ending up on dialysis over the next 2-5 years. 

Patients come in and they are worried because they looked at their lab results and see that their creatinine level is red, or their eGFR is low. They think, It says I have stage 3a CKD. 

We should probably have the stages of CKD start at stage 3, which should be called stage 1 so it doesn’t sound as bad. Patients think they are halfway to dialysis; they are already at stage 3 and didn’t even know their kidneys were a problem. 

Dr Topf said that cystatin C (something I only recently started ordering) can be obtained, and sometimes you can recategorize the patient, especially those with an eGFR between 45 and 60. The cystatin C can predict their renal function better than the creatinine-based equations. If you are using the creatinine equation, he recommends using the 2021 equations. 

Another nice thing about cystatin C is that it isn’t tripped up in younger patients with a lot of muscle mass. You just have to watch out for inflammation, which can throw the test off. For example, when a patient is in the intensive care unit, it’s probably not that helpful, but for your outpatients, cystatin C works well. 

Williams: I’ve been using it a fair amount in my patients with more muscle mass. And some patients have been taking creatine as a supplement, and that can alter the numbers as well. This is a nice way to get them out of CKD stage 2 or 3 and back where they belong, with normal healthy functioning kidneys.

Watto: Now, Paul, if we find a patient with more advanced CKD — let’s say stage 4, whether by cystatin C or serum creatinine, and their eGFR is less than 30 — should we start peeling off the angiotensin-converting enzyme ACE inhibitor or the angiotensin receptor blocker (ARB)? Those drugs can raise potassium. What should we do here? 

Williams: That’s the temptation, Matt, and I feel like that was the old orthodoxy, back in residency. It didn’t take much for us to start taking off ACE inhibitors or ARBs once the kidney function started to drop, but it turns out you may be doing more harm than good.

Some data have shown that if you peel off those medications, you actually increase mortality and cardiovascular risk. So, in general, if you can keep them going, the patient will be better off. Hang onto the ACE inhibitors or ARBs as long as you are able to, because they confer a fair amount of benefit.

Watto: As long as the potassium isn’t in red on your lab’s range. It might go up to 5.2 or 5.4, but as long as it’s stable, that should be OK. You probably wouldn’t initiate an ACE inhibitor or ARB or spironolactone with a potassium level above 5, but if it’s below 5 when you start and it goes up slightly after you start the drug, that could be acceptable. 

Another thing we talked about was when a patient progresses to CKD and ends up on dialysis, how helpful are those intradialysis blood pressures in predicting cardiovascular outcomes? 

Williams: For someone who’s performing the dialysis, probably really helpful. In the outpatient setting to predict cardiovascular risk, probably less so. Dr Topf makes the point that the readings are done either shortly after or right when the patient is about to have a large-bore catheter inserted into their arm. And then they have liters of fluid drained out of them. So those numbers are going to have huge amounts of variability. You would not base the patient’s blood pressure treatment solely on those numbers. But regardless of what the numbers are, or even regardless of your office numbers, hopefully you’re working with a nephrologist to make sure that you’re actually in concert and not fighting each other with the blood pressure medications.

Watto: Dr Topf said that a lot of the hypertension in dialysis is because of too much volume. If you can get the volume down, you might be able to peel off blood pressure medications instead of adding more. But some patients have issues with cramping; it’s uncomfortable and not everyone tolerates it. 

I was really surprised to learn that beta blockers, specifically atenolol, have some evidence of improving cardiovascular outcomes in patients on dialysis. Dr Topf speculated that this was because they are largely dying of cardiovascular disease, so maybe that’s why, but that’s one of the places, the only places I can think of aside from thyroid disease, where atenolol really shines. 

If you want to hear this fantastic episode and all the great pearls, then click on this link.