Doctor,
I just wanted to put in my two sense and see what you think. I think that lab calculations of eGFR in most labs is totally inaccurate. Most labs use the standard MDRD formula to calculate eGFR. This equation is a standard equation that does not take into account for muscle mass, weight, height, etc. It is a formula that uses the average height and weight for the average male from the 1920s! It has been stated that the MDRD equation can be off by 29% in healthy patients. The National Kidney Foundation suggests using the CKD-EPI Creatinine Equation (2009) to estimate eGFR. This equation takes into account height, weight, age, etc.
I have been worried about my kidneys now for the last couple years. I'm 39 years old white male, 6'3" tall and weight 205 lbs. I weight train six days a week. I USED to take creatine suppplements. About two years ago I went in just to have a simple check up. They ran my blood and my GFR came back at 38! I was totally freaked out. The doctor told me to quit taking the creatine supplement and come back in two weeks. After two weeks, I tested again and my GFR was 58. The doctor said it was improving and I should be fine. Since then I always have had this worry that something is wrong with my kidneys. I constantly look at the toilet after urinating to see if there are any bubbles or foam. I have had blood work done 4 times since them and had about 3-4 urine tests. They have never found protein in my urine from urine tests. I also had microalbumin tested and it came back "unable to calculate" with my microalbumin reading being <12.00 mg/L. I also had CT scan of my kidneys and also had a CT scan of kidneys where they used contrast dye. The radiologist stated that kidneys were functioning well for filtering the dye. I also had an ultrasound done on my kidneys and came back as normal. I have seen several doctors and even went to a renal doctor, which by the way wasn't available so they had me see a nurse practitioner instead who works in the renal office. When I was visiting that nurse, they did my bloodwork and my Creatinine came back as 1.36 and GFR was like 58 again. During all of this, my follow up tests have basically came back in this range. My very last test that I had done about six weeks ago came back at Creatinine 1.26 and GFR came back as normal (which means it was above 60 GFR). With that said, the renal nurse at that time actually diagnosed me with Stage III kidney disease, so of course this freaks me out even more. Their lab uses the standard MDRD equation. I began to do more research online and came across the National Kidney Foundation and the CKD-EPI equation that they recommend to use. Also found several other sites that state that the MDRD equation is outdated.
So, here is my question for you. When I enter my numbers, height, weight, age, into the CKD-EPI equation I get GFR of 91, which for my age the range is 90 to 100 for normal. Furthermore, I did even more research on why there is an option to select African American or non African American when using these calculators. I found out that the reason for this is because most African Americans of the same size, age, and height have an average of 20% more muscle mass than other races. So, this is something that I also should consider or else why would there be this option? Muscle mass does make a difference or else it would not be an option when calculating GFR. I'm not the average muscle mass of someone the same race, age, and size. I'm pretty lean and have larger than average muscle mass from weight training. So, if I check the African American box on the GFR calculator, I come back at 106 GFR. But for argument sake, lets just say I'm not the 20% more muscle mass and take half of that, my GFR would be 98.5. Do you think that the way I'm looking at all of this and trying to calculate my GFR is accurate? To me, it seems totally reasonable to use the height, weight,and muscle compostion of the person actually being tested, and not to use the height, weight, and muscle composition of someone that is much smaller. Lastly, I do eat a higher protein diet which I have read can contribute to higher creatinine levels along with muscle breakdown from working out almost every day.
I guess I'm looking for your opinion here as it worries almost every day. Most of the doctors I have seen (except for the renal nurse which is very surprising) say that I'm fine and to quit worrying about it. It just amazes me that these generalized equations used in many labs are not more specific and may be wrongly diagnosing people with kidney disease?