Low EGFR with muscle mass

[Reegor]

I'm a male 50 and recently had blood tests with EGFR of 56. 2 other tests have 59 then 55. Going back through 10 years of results I've never been over 74. No symptoms. Had ultrasound on kidneys and perfect for shape, size, and blood flow.

Creatinine slightly high at 1.38. Rest of values are perfect. Non drinker health nut. Needless to say this freaked me out a bit.

After research, research and more research. (Remember kind of freaked out) I guess the EGFR is a calculation using age and other factors along with creatinine levels.

Creatinine levels can be higher in people with a lot of muscle from what I gather. Example: So if I'm 282lbs at 50 years old but my BF is 13% it means I have quite a bit of muscle and the EGFR may not be very accurate. I read I should actually be looking to get a Cystatin 3 Blood Test. It isn't as prone to false calculations with people with muscle mass or people that eat meat.

Anyone else come across a similar issue? Anyone with low EGFR but may have high muscle % and have this issue? Anyone get a Cystatin 3 blood test? Results?

[rabbit01]

Yes you are correct. If you think about creatinine in the same way as exhaust fumes from a car then even at tick over a 5 litre high performance engine is going to put out more waste products than a 1 litre engine. So yes if you have above average muscle mass then your creatinine is going to be naturally a lot higher than someone who has a small muscle mass.

[Barbee44 in reply to rabbit01]

So, I was a walker and biker for 10 yrs...I have a lot of muscle in my legs. I just had spinal surgery and now more bulging discs. I can't exercise.... could my GFR be low because I'm losing muscle mass?

[rabbit01 in reply to Barbee44]

I would not know the answer to that but certainly worth checking with your doctor.

[bikerchrish]

I know this is a 4 year old post but what news is there about your egfr with muscles? I have stage 3 ckd but I have muscles and this interests me.

[Marvin8]

Just as another data point, I'm 64, slight of build, but muscular....ie...5'6" and 145lbs. My Cystatin-C (not 3) gives me an eGFR 30 points higher than my creatinine eGFR. My nephrologist doesn't give a whole lot of weight to the Cystatin-C formula, but from all the research I've done, the combination formula (creatinine + Cystatin-C)/2 comes closest to actual measured GFR. That being said, the major fly in the ointment for Cystatin-C is your thyroid. If one has even a slight thyroid issue, the Cystatin-C formula is pretty much worthless. And most doctors never run a comprehensive full panel thyroid test. My last creatinine eGFR was 56 while my Cystatin-C was 85 which gave me a combined eGFR of 70. I'm a little bit suspicious of my thyroid though.