Supplements
A lifter gets his bloodwork back. Creatinine is above range. eGFR has dropped into the band labelled as reduced kidney function. The report suggests following up. He has been taking creatine for two years, trains five days a week, and feels completely fine.
In most cases like this, nothing is wrong with his kidneys. The test is measuring exactly what it is designed to measure, and the interpretation is wrong.
Creatine is the supplement. It sits in your muscle as phosphocreatine and helps regenerate ATP during short, hard efforts. It is the most researched supplement in sport and one of the few that reliably works. If you are topping up, plain micronised creatine monohydrate is all you need — no proprietary blend improves on it, and you can get one from God of Supps.
Creatinine is a waste product. Creatine breaks down into it spontaneously, at a rate of roughly one to two percent of your total creatine pool every day. Your kidneys filter it out and it leaves in urine.
One letter apart, completely different molecules, and the relationship between them is the entire source of the problem.
Follow the chain. You supplement creatine. Your total creatine pool increases, which is the point of taking it. A fixed percentage of that pool converts to creatinine every day. A bigger pool means more creatinine produced. More creatinine produced means more of it in your blood.
Your kidneys are clearing it perfectly well. There is simply more of it arriving.
The rise is usually modest, but it does not need to be large to matter, because of what happens next.
Labs do not measure your kidney function directly. Measuring it properly requires an infused tracer and a research setting, so in practice nobody does it. Instead, they estimate it.
The estimated glomerular filtration rate, eGFR, is calculated from a formula whose main input is your serum creatinine, adjusted for age and sex. So if creatinine rises for any reason, eGFR falls automatically. The formula has no way of knowing why the creatinine went up. It assumes reduced filtration, because that is the usual cause in the general population the formula was built from.
That population was not full of people taking creatine and carrying a lot of muscle.
This is worth understanding even if you never touch creatine. Creatinine production is proportional to muscle mass. A 95 kg lifter produces more of it than a 60 kg sedentary man of the same age, every day, with identical kidney function.
The eGFR formula does not ask about your body composition. It sees a higher creatinine and reports a lower filtration rate. Being muscular alone can put a healthy person into an apparently abnormal band. Add creatine supplementation on top and the effect compounds.
This has been looked at repeatedly, because the question keeps coming up. Controlled trials in healthy adults, including studies running for several years, have consistently failed to find evidence of kidney damage from creatine at standard supplemental intakes. What they find is the creatinine rise described above, without any of the markers that accompany genuine renal impairment.
The position taken by the International Society of Sports Nutrition, in their position stand on creatine, is that it does not cause renal dysfunction in healthy individuals. That is a meaningful distinction. In healthy individuals. Somebody with existing kidney disease is a different conversation and belongs with their nephrologist, not with a supplement article.
If you want to know whether your kidneys are actually fine, ask for cystatin C.
Cystatin C is a protein produced by essentially all nucleated cells at a steady rate. Unlike creatinine, it is not meaningfully affected by muscle mass, and it is not affected by creatine supplementation at all. eGFR can be calculated from it using the same kind of equation.
If your creatinine-based eGFR looks low and your cystatin C-based eGFR is normal, you have your answer: the creatinine was the artefact.
It costs a few hundred rupees in most Indian labs and it is almost never included in a standard package. You have to ask for it by name. The blood test selector flags markers like this, the ones that answer a specific question and never appear on a full body checkup.
Creatinine on its own is a weak signal. Read it alongside:
If creatinine is up but albumin is not leaking, cystatin C is normal, and electrolytes are fine, the picture is reassuring. The bloodwork analyzer reads kidney markers together rather than flagging creatinine in isolation, which is what most lab reports do and why they cause unnecessary alarm.
Three things affect the result and all of them are controllable.
Stop creatine for five to seven days before a panel if you want a clean creatinine reading. This is the simplest way to separate supplement effect from anything else.
Do not train hard for 48 hours beforehand. Intense exercise causes muscle turnover, which raises creatinine independently.
Be properly hydrated. Dehydration concentrates everything in the blood, creatinine included.
Ignore all three and retest, and you will get a different number, which teaches you nothing.
None of the above means every raised creatinine is harmless. Take it seriously if:
A stable, modestly raised creatinine in a healthy muscular person taking creatine is a different situation to a climbing creatinine in someone with diabetes. The tests above tell you which one you have.
Creatine raises creatinine because creatinine is what creatine turns into. eGFR is calculated from creatinine, so eGFR falls on paper. Neither of those is kidney damage. Muscle mass does the same thing independently, which is why lifters see this more than anyone.
If you want certainty rather than reassurance, ask for cystatin C and a urine albumin to creatinine ratio. Two cheap tests, and they answer the question properly.
In healthy individuals, controlled research has consistently found no evidence of kidney damage from creatine at standard supplemental intakes. It does raise serum creatinine, which is a measurement effect rather than an injury. People with existing kidney disease should discuss it with their doctor.
Creatine breaks down into creatinine at a roughly fixed daily rate. Supplementing increases your total creatine pool, so more creatinine is produced and more appears in your blood. Your kidneys are clearing it normally, there is just more of it.
On paper, yes. eGFR is calculated from serum creatinine, so anything that raises creatinine lowers the calculated eGFR automatically. Actual filtration is unchanged, which is why a cystatin C-based eGFR is the useful cross-check.
If you want a clean creatinine reading, stop five to seven days beforehand, avoid hard training for 48 hours, and be properly hydrated. Otherwise the result reflects the supplement and the training rather than your kidneys.
A protein produced at a steady rate by most cells in the body, used as an alternative marker of kidney filtration. It is not affected by muscle mass or creatine supplementation, which makes it the better test for anyone who trains.
Yes. Creatinine production is proportional to muscle mass, so a heavily muscled person produces more of it with identical kidney function. The eGFR formula does not account for body composition, so muscular people can appear to have reduced function when they do not.
This article is educational and is not medical advice. See the medical disclaimer.
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