In Chinese medicine winter is the season associated with the kidney. So when you start to think about supporting your health in the new year, your kidneys are an excellent place to start. While spring is the best time for a liver detox, cleaning up your diet in the new year helps both your liver and your kidneys, and every other part of you!
When it comes to blood tests you may have noticed our focus is not just on absolute numbers, but also trends. This is all the more true for kidney function tests, and here’s why:
The kidney’s main function is to filter our blood, excrete what we don’t want, and reabsorb what we need. The structures in the kidney that do the filtering are called glomeruli, and one of the things they filter out for excretion is creatinine.
Creatinine is a waste product made when you use your muscles, so we all make it all the time. Generally, if blood levels of creatinine are high, the kidneys aren’t working well. Indeed we can estimate how well they are working, calculating from the level of creatinine still circulating in our bloodstream, rather than filtered out. This is why our kidney function test is called the estimated glomerular filtration rate, or eGFR.
However, the eGFR does vary depending on how active we have been, as well as how hydrated we are. We make more creatinine when our muscles have been more active, whether that was running a marathon, running after toddlers, or any form of vigorous exercise. (That’s a rarity: bloodwork that, if in a higher range than normal, may be due to something good going on!). If we are dehydrated, the concentration of everything in our blood is higher, including creatinine. It may be as simple as a need to drink more water.
We therefore advise that if you get one kidney function test that doesn’t look good, think about what you were doing before you did the test. Get another test done when you have been less physically active and are well hydrated. It’s only after two or three questionable blood test results that we can conclude there is cause for concern.
Creatinine and the eGFR can be a bit counter-intuitive, and therefore confusing. You see, creatinine and eGFR are inversely proportional: if blood levels of creatinine are high, the eGFR will be low. That’s because the kidney isn’t filtering creatinine out well, so that tells us that kidney function is low. Conversely, if creatinine is low, the kidneys are doing a fine job!
You may have seen the eGFR on your blood test results and wondered how to read it. The first thing to note is that eGFR is not a percentage result like an exam at school. Although 100 is excellent, 60 tells you there may be something to start paying attention to, and 40 indicates a problem, this is not a percentage: occasionally people’s eGFR comes in at 110!
An eGFR greater than 60 is considered a normal result. If your result is lower than that, your kidney function is not optimal. While it’s not deeply concerning, it should be monitored regularly: a downward trend is cause for concern.
Kidney function is known to decline gradually as we age, and the calculation of the eGFR from creatinine is adjusted slightly according to how old we are.
Because we don’t feel any effects from low kidney function until it is dangerously low, it’s a good test to understand and track on a graph. We do expect a gentle decline with age, but we don’t want to see it going down dramatically, and we want any anomalies to be accounted for by circumstances at the time of the test.
And remember, only be concerned if several tests show the eGFR to be trending low.
Western medicine has little to offer to support kidney health. It focuses on diet to reduce the load on the kidneys (which is always a good thing), and reducing high blood pressure with medication, to protect the delicate structures of the kidneys. More intense intervention is given when the kidneys are in failure, either dialysis (using a machine to replace the kidney’s filtering function), or later a transplant: dire circumstances!
Naturopathic doctors prefer to intervene more gently at an earlier stage. If someone’s kidney function is declining, we give herbs to support kidney function, and drainage remedies to clean toxins out of the kidneys so they can work better. And we use the eGFR to monitor their benefit!
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