Creatine and your blood values: why creatinine rises without kidney damage

Your result lands in your inbox. Creatinine 110 µmol/l, with an arrow pointing up next to it. You search for high creatinine, and within two minutes you are reading the words kidney damage.

I think this is the most annoying false alarm in men's blood testing. Two words that differ by a single letter, creatine and creatinine. The fright arrives instantly.

Creatine, the stuff in your shaker, raises the creatinine your lab measures. That number is a waste product from your muscles. It is not proof that your kidneys filter worse.

Why does creatine raise your creatinine?

Your body stores creatine in your muscles, where it slowly breaks down into creatinine. Take 5 grams a day and there is simply more creatine available to break down. So more creatinine ends up in your blood, while your kidneys keep working exactly as hard as before.

Your muscles use creatine phosphate as fast energy. Every day, roughly 1 to 2 percent of your creatine store breaks down into creatinine. That waste product enters your blood, and your kidneys sieve it out.

More creatine in your muscles means more waste product per day. Your creatinine can rise slightly as a result, often in the range of 10 to 30 µmol/l. The ISSN described this in 2017 as a measurement effect, not as damage (PMID 28615996).

It is a bookkeeping difference, not a medical one.

Creatine or creatinine: one letter apart

Your result almost never says creatine. It says creatinine, with the extra letters, and that is the waste product your muscles make day and night, measured in µmol/l. Creatine is the supplement in your kitchen cupboard, and a standard kidney panel does not measure it at all.

If you search for a high creatine value, you almost certainly mean your creatinine value. The same goes for a normal creatine value. What you want is the normal range for creatinine.

There is a third word that looks similar: creatine kinase, or CK. That is a muscle enzyme that can spike hard after a heavy session. It is another thing again, and not a kidney value.

What is a normal creatinine value?

In adult men, creatinine usually sits somewhere between 60 and 110 µmol/l, depending on the lab. Women sit lower, because they carry less muscle mass on average. So always read the reference range printed on your own result, since those borders differ per laboratory.

Muscle mass is the big disturber of this number. A muscular man of 95 kilos makes more creatinine per day than a slight man of 65 kilos. Both can have perfectly good kidneys, with a very different creatinine on paper.

A value just above the upper limit therefore says little on its own. It says something about how much creatinine you produce, not only about how much your kidneys clear. How to read that result next to your eGFR is covered in our piece on creatinine and eGFR.

How high can your creatinine be on creatine?

There is no separate reference range for men who take creatine. What changes is not the border, but the meaning of a number above it. A slightly raised result fits with plenty of muscle mass plus daily creatine, and need not mean a kidney problem.

Take two men with exactly the same result: creatinine 110 µmol/l. The first weighs 90 kilos, trains heavy four times a week and takes 5 grams of creatine a day. The second sits still most of the day and carries little muscle.

Same number, two very different stories.

In the first man, the extra creatinine is easy to explain. Plenty of muscle, plus a supplement that breaks down into exactly this substance. In the second man that explanation is missing, and the number deserves more attention.

Antonio and colleagues call this one of the most stubborn misconceptions around creatine (PMID 33557850). The number rises. Your kidney function need not fall with it.

What does creatine do to your eGFR?

Your eGFR is not measured but calculated, usually with the CKD-EPI formula. That formula takes your creatinine, your age and your sex as input. If your creatinine rises on creatine, a lower eGFR rolls out automatically, even though nothing changed inside your kidneys.

An eGFR below 60 ml/min/1.73 m² generally counts as a point of attention. In a muscular man taking creatine, that figure can come out artificially low. The formula knows nothing about your shaker or your squat rack.

So a low eGFR in lifters is more often a false alarm than in non-lifters. It is a shift in the arithmetic, not an organ problem. What creatine does to your various kidney values is set out below.

Cystatin C: the kidney value creatine does not distort

Cystatin C is a small protein that nearly all your cells make at a steady rate, not your muscles. Your muscle mass and your creatine use barely influence it. So cystatin C gives a second view of your kidney function, exactly where creatinine can fall short in muscular men.

What strikes me is that this word barely appears in the search results about creatine and kidneys. That is a shame, because it is the value that settles the argument. Shlipak showed in the New England Journal of Medicine that cystatin C sometimes estimates risk more sharply than creatinine alone (PMID 24004120).

In practice it is simple. Your creatinine mixes up what your muscles make with what your kidneys clear. Cystatin C takes your muscles out of that equation.

That makes it a useful second value for the muscular man with a raised creatinine. If you want to see your kidney values side by side, you can look at our kidney function test. Your GP can then help you decide whether further steps are needed.

Is creatine bad for your kidneys?

In healthy people, research so far has found no signs that creatine damages the kidneys. The ISSN wrote in 2017 that creatine monohydrate has not been linked to kidney damage in healthy users (PMID 28615996). If you have a known kidney disease, the picture differs, and you discuss this with your doctor.

Poortmans and Francaux followed athletes who used creatine for up to five years. Their kidney function did not decline over that period (PMID 10449011). That is no guarantee for everyone, but it weighs more than a forum story.

The Dutch Voedingscentrum counts creatine among the sports supplements with a described effect on short, explosive effort. It also points out that taking more does not give you more, because your muscles reach saturation. Go far above the usual 3 to 5 grams a day and you mostly buy expensive urine.

When is a high creatinine an actual signal?

A raised creatinine does deserve attention when it keeps climbing on repeat tests, or when other values move with it. Think of protein or albumin in your urine, a rising urea, or symptoms like foamy urine and swollen ankles. Then the picture fits your kidneys better than a supplement.

According to the Dutch Nierstichting, around 1.7 million people in the Netherlands live with chronic kidney damage, often without knowing it. That damage rarely starts with one odd number after a month of creatine. It builds over years, usually alongside high blood pressure, diabetes or cardiovascular disease.

Urea belongs in this list too. Urea comes from your protein metabolism and does not move with creatine. If it stays normal while your creatinine climbs, that points at your muscles more often than at your kidneys.

In doubt? Then this conversation belongs with your GP, not with a forum.

What you can do before your blood draw

The simplest thing you can do: tell your doctor and the lab that you use creatine, and how many grams a day. Without that context, a raised creatinine reads very differently. Some men choose to stop a few weeks before the draw, so their value does not move with their supplement.

Creatine does not leave your muscles in a day. After stopping, it takes an estimated four to six weeks before your store returns to your own baseline. A break of two to three weeks already removes a good chunk of the effect.

Two things many men forget. A heavy leg session the day before can lift your creatinine temporarily. So can a big steak the night before, since meat simply contains creatine.

Eating a lot of protein does something similar to your urea. How much protein you actually need is covered in our piece on protein shakes. How protein and creatine act on your kidneys together is covered in protein, creatine and your kidneys.

Seeing a raised creatinine while you take creatine? Ask your GP whether adding cystatin C makes sense, and tell them how much you take and how heavily you train. I would never leave that last part out, because it changes the whole reading of your result.

Which supplement you actually need, and which blood value tells you, is covered in our overview of supplements for men.

References

• Kreider RB, et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation. J Int Soc Sports Nutr. 2017. PMID 28615996.
• Poortmans JR, Francaux M. Long-term oral creatine supplementation does not impair renal function in healthy athletes. Med Sci Sports Exerc. 1999. PMID 10449011.
• Antonio J, et al. Common questions and misconceptions about creatine supplementation. J Int Soc Sports Nutr. 2021. PMID 33557850.
• Shlipak MG, et al. Cystatin C versus creatinine in determining risk based on kidney function. N Engl J Med. 2013. PMID 24004120.
• Voedingscentrum. Sports nutrition and supplements. 2024. voedingscentrum.nl
• Nierstichting. Chronic kidney damage in the Netherlands. 2024. nierstichting.nl

Every blood test result at Caliber includes a professional assessment by a BIG-registered doctor. For treatment decisions, always discuss your results with your GP.