Creatine has become one of the most popular and well-researched supplements available. Yet people taking it regularly are sometimes told by their doctor to stop because their blood tests suggest their kidneys are being damaged. This article explains why that interpretation is usually wrong, what those tests are actually measuring, and what the research really shows.
What Is Creatinine and Where Does It Come From?
Creatinine is a waste product from normal muscle activity. Your muscles constantly produce small amounts of it as a byproduct of using creatine for energy. It moves out of muscle cells into the bloodstream, and healthy kidneys filter it out and flush it away in the urine.
Because healthy kidneys clear creatinine efficiently, a build-up in the blood is generally a sign the kidneys aren’t filtering properly. This is why blood creatinine is used as a marker of kidney function.
However, blood creatinine is also directly influenced by:
- Muscle mass: more muscle = more creatinine produced
- Diet: meat and fish contain 4–5 g of creatine per kg
- Exercise intensity: hard workouts temporarily accelerate creatinine production
- Creatine supplementation: a typical 5–10 g supplement dose is equivalent to eating 1–2 kg of meat
Normal reference ranges are approximately 60–105 µmol/L for adult males and 45–90 µmol/L for adult females (New Zealand).
Why Does Creatine Supplementation Raise Blood Creatinine?
When you supplement with creatine, you increase the total creatine pool in your muscles. Since creatinine is produced by the spontaneous breakdown of creatine and phosphocreatine, a larger pool means more breaks down into creatinine each day, simply because there is more available.
The result is a slightly but stably elevated blood creatinine level. This is not because the kidneys are failing. The kidneys are still clearing creatinine perfectly well, they are just clearing more of it. Think of it like turning up a tap slightly: the water level in the bath rises until it reaches a new equilibrium, with the drain working just as well as before.
This elevated creatinine can look like mild kidney impairment on a blood test, even though kidney function is completely normal.
What Is eGFR and Why Is It Affected?
From your serum creatinine, doctors calculate an estimated Glomerular Filtration Rate (eGFR), a number representing how well your kidneys are filtering blood. The standard equation used (called CKD-EPI) uses serum creatinine, age, and sex.
The equation is built on population averages. It assumes that an older person or a woman has lower muscle mass and therefore lower creatinine production, so the same creatinine level in an older woman is interpreted as a sign of worse kidney function than it would be in a young muscular man.
This means the equation can be significantly misled when creatinine is elevated for non-kidney reasons. A falsely high creatinine input produces a falsely low eGFR output.
The Perfect Storm: Older, Muscular, High Protein, Taking Creatine
Consider someone who is an older woman, has above-average muscle mass, eats a high-protein diet, and takes creatine. Every one of these factors independently pushes creatinine up and eGFR down:
- Higher than average muscle mass — more baseline creatinine production than the equation expects for her age and sex
- High protein diet — dietary creatine from meat and fish increases the creatine pool further
- Creatine supplementation — adds directly on top of this
- Older age with higher than average muscle — the equation applies an age correction assuming low muscle mass, so her elevated creatinine is interpreted as significantly impaired kidneys
The result can look alarming on paper, yet her kidneys may be functioning perfectly.
What About the Urine Albumin/Creatinine Ratio (ACR)?
Routine kidney checks in New Zealand also include a spot urine test measuring the albumin-to-creatinine ratio (ACR). Albumin is a blood protein that healthy kidneys should retain, and only a trace amount should appear in urine. A raised ACR is a marker of genuine kidney damage.
Creatine supplementation does not raise urinary albumin. In fact, because creatine increases urinary creatinine (the denominator of the ratio), ACR may appear slightly lower in people supplementing, which is the opposite of what you’d typically see in kidney disease.
A normal ACR is less than 2.5 mg/mmol for men and less than 3.5 mg/mmol for women.
What Does the Research Actually Show?
Studies consistently show that creatine supplementation raises serum creatinine and lowers calculated eGFR. However, remember, this is and estimate of GFR via a calculation – not a direct measurement.
A recent meta-analysis found that while serum creatinine increased with creatine supplementation, there were no significant changes in measured GFR (the direct, non-estimated measurement of kidney filtration).
The International Society of Sports Nutrition (ISSN) concluded:
“Experimental and controlled research indicates that creatine supplementation, when ingested at recommended dosages, does not result in kidney damage and/or renal dysfunction in healthy individuals.”
A Better Test: Cystatin C
If there is genuine uncertainty about kidney function, Cystatin C is a far more reliable alternative. It is a protein filtered by the kidneys whose blood levels are unaffected by muscle mass, dietary protein, or creatine supplementation. An eGFR calculated using Cystatin C (rather than creatinine) is considered the gold-standard option when lifestyle factors are confounding creatinine-based results.
Practical Advice
If you are taking creatine and have an upcoming blood test:
- Tell your doctor you are taking creatine – this context is essential for interpreting results correctly
- Avoid testing immediately after a hard workout – exercise temporarily elevates creatinine
- Make sure you are well hydrated – dehydration artificially raises creatinine
- Consider stopping creatine for 5–7 days before retesting to establish your baseline
- If your doctor is concerned or results are unclear, ask about Cystatin C testing
Should People With Kidney Disease Take Creatine?
This article applies to healthy individuals. If you already have diagnosed kidney disease or impaired kidney function, you should consult your doctor before taking creatine.
Summary
Creatine supplementation raises blood creatinine and lowers calculated eGFR, but this reflects increased creatinine production, not kidney damage. The standard kidney function equations were not designed with muscular, high-protein, creatine-supplementing individuals in mind, and can produce misleading results in this population. Multiple well-controlled studies confirm that creatine does not damage kidneys in healthy people. If your doctor is concerned about your results, this article and the research cited within it, may help inform that conversation.
References:
- Meta-analysis on creatine and measured GFR: https://pmc.ncbi.nlm.nih.gov/articles/PMC12590749/
- National Kidney Foundation on eGFR: https://www.kidney.org/atoz/content/gfr
- ISSN position on creatine safety: https://link.springer.com/article/10.1186/s12970-021-00412-w