Simple explanation of alteration in kidney function tests while on the MP
A lot of MP patients get worried by low eGFR and highish creatinines, and experienced MP doctors know its not important. Here's a short explanation which I hope helps to explain whats going on.
How to understand the relationship between serum creatinine, eGFR, and creatinine clearance:
Think of the serum creatinine level as a water level in a river. Its a spot measurement.
Think of the 24 hr creatinine clearance as the actual amount of water flowing down the river over 24 hours. This has been measured in your case.
Think of eGFR as a calculation or projection of the water flow, based on the spot measurement of the water level. This is highly inaccurate in certain circumstances, due to several important factors left out. The main assumption is that it never 'rains'.
But on the MP, the harder you herx, the more it 'rains'. So the water level (the serum creatinine) rises. But in most people on the MP, the river flow is not compromised at all (ie kidney function as measured accurately by 24 hr creatinine clearance) . We already know this intuitively because we know that its 'raining', ie that you are having high cell turnover and making a lot of creatinine due to herx. And we can know this deductively because you did a 24hr urine, and measured the amount of creatinine cleared in 24 hrs, which was completely normal.
So, when on the MP, serum creatinine and especially eGFR are really NOT showing what is going on. Much more important is 24 hr creatinine clearance. When 24 hr creatinine clearance is normal, then you know that you can ignore eGFR and serum creatinine, because they are only telling you how hard it is 'raining', and not how well your kidneys are functioning at all.
And those who do have real kidney impairment need to be checking 24 hr creatinine clearances and spot potassium levels. Potassium levels are very important to cardiac function, and high levels or low levels can trigger cardiac arrythmias.
Personally in most MP patients, I would more likely order a 24 hr creatinine clearance for a rising potassium level than a rising creatinine level on its own. Rising creatinine on its own needs to be managed as a sign of herxing, and managed by modulating the herxing in the usual way (increase olmesartan, adjust antibiotics etc).
I hope this helps you understand the numbers and what they do and do not represent. ~Dr. Nyrie Dodd
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* We can help you understand chronic disease, but only your physician is licensed to give you medical care * Always consult your physician before commencing or changing any treatment he/she has prescribed for you
