Chronic kidney disease has become an under appreciated epidemic in itself and it largely mirrors and has been driven by our ever growing diabetes epidemic. Many people that engage in relatively high protein diets will see an elevated BUN level on their lab panel and may feel that as a flag for concern and in some instances it can be, in other instances it is a normal and expected variation. Let’s talk about how we can sorts things out.
While in truth the kidneys are incredibly complex organs with a wide variety of functions, their basic function remains as a selective filter that eliminates and retains substances within our bloodstream.
What is blood urea nitrogen (BUN)?- Urea nitrogen is a byproduct of protein metabolism and is produced by the liver and filtered by the kidneys, elevated levels can be caused by heart failure, infections, kidney disease, drug usage, stress, heart attacks, pregnancy, burns and shock as well as aging. Another common non pathological cause is a high protein diet. Like all lab numbers we have to take things into clinical context before we make a conclusion as to their meaning.
As most of you know I follow a fully carnivorous diet and ingest plenty of protein in the form of delicious ribeye and T-bone steaks, in general I consume anywhere from 300-600 grams of protein a day and have done so for about a year and a half. At my current bodyweight of about 250lbs that translates into around 3-6 gm/kg per day, definitely a hefty dose. Now we have seen a number of studies recently that have seen younger athletes being looked at with similar protein loads with no evidence of kidney dysfunction, but what about me, as a 50 plus year old athlete?
I recently had some labs taken and among those labs it was noted that my BUN was slightly elevated at 29 (with a normal top end range on that particular assay being 25). Now of course the interpretation by some of the vegan activist proponents was obvious impending kidney failure, followed by a few anemic chants of “meat is murder”.
So is there an easy way to sort this dilemma out? Am I on my was to an early grave or thrice per week visits to the dialysis center or is it just an expected finding from eating a protein rich diet?
What other info do we have? Now any good clinician will look at a lab value and then will figure out if it is something is concerning or not. Now we already know that I eat plenty of protein and also train very hard and carry a lot of muscle mass so those things alone can easily explain the slightly elevated BUN. But fortunately we have even more information to look at in the lab data that tells us my kidneys are functioning just fine.
GFR (estimated)-another basic measure to understand someone’s renal function is the glomelular filtration rate(GFR)- this is a basic snapshot at how efficient one’s kidneys are at doing their filtration job. Now fortunately for me, and disappointingly for my vegan fans, I also had my GFR tested and it came back in the normal range. One interesting point about the GFR, is that it is just an estimate and not a direct measurement. The commonly used MDRD formula to determine this is based on ones serum creatinine one’s age, sex and race and assumes one’s body surface area is equal to 1.73 square meters. The reason you always see a higher number for African Americans is that it is assumed they carry a greater proportion of lean muscle compared to other races. Also when we see that anything over 60 ml/min/1.73m2 is considered normal using this formula because it fails to account for overall body size and lean muscle mass among other things. As my value was above 60, this indicates normal function- Now, if I wanted to get an even better estimate I could calculate my actual body surface area which is much higher than the generic person (1.73m2) and see an even better/higher GFR, (at 6’5” 250lbs my BSA is around 2.5m2), and if we also could account for the fact that I am also leaner and more muscular than Mr. Generic human (BSA 1.73) we’d see an even further higher estimate of my GFR.
What about using another formula that takes into account bodyweight? Yes fortunately that formula exists as well and again uses the serum creatinine as well as ones bodyweight. This is called the Cockcroft-Gault formula and it determines another estimate of renal function called creatinine clearance. Let’s plug my numbers into this formula and see how my kidney function stacks up. Plugging in my numbers (51 years, male, 250lbs, serum creatinine 1.2) yields a creatinine clearance of 116- the normal range for males is 97-137ml/min which puts my value perfectly in the middle of this range!
So in my case, since I haven’t been recently burned, haven’t had a heart attack (sorry vegans) and am not pregnant, the slight elevation in BUN does not in anyway indicate kidney disease and just reflects eating plenty of protein. As I’ve said repeatedly our labs are something that can change from day to day and also have got to be taken in context. Next, time we will go over my blood lipids. Until then take care enjoy that steak medium rare, your species earned it!