My GP told me to stop taking creatine. Here’s what they were probably confusing.
A raised creatinine reading on a routine blood test is sending thousands of people off creatine supplementation every year, most of them unnecessarily. Here is what is actually happening, why the test has a blind spot, and what to ask your doctor instead.
You get your routine blood results back. There’s a note from your GP. Your creatinine is elevated, your eGFR looks off, and the advice is clear: stop taking creatine.
You stop. Of course you do.
This scenario is playing out every day in GP surgeries across the country. And in the vast majority of cases, the kidneys are completely fine. What’s happening instead is a case of mistaken identity… one that the science has understood for years, but that has not yet made it reliably into the ten-minute appointment.
This piece explains the confusion, why it matters, and what to do about it.
First: creatine and creatinine are not the same thing
They are related, and that is exactly where the confusion begins.
Creatine is the compound you supplement. It is also synthesised naturally in your body (in the liver, kidneys and pancreas) from amino acids, and stored predominantly in your muscles to produce energy rapidly during intense effort. Its clinical safety record spans more than forty years and over 680 peer-reviewed trials.
Creatinine is a waste product; the breakdown residue after your muscles use creatine phosphate for energy. It is constantly produced, filtered by the kidneys, and excreted in urine. It is also the molecule that doctors measure in your blood as a proxy for how efficiently your kidneys are filtering.
Here is where the problem starts. When you supplement with creatine, you increase the total creatine pool in your body. More creatine in the system means more creatinine is produced as a byproduct. This is a normal metabolic consequence, and not necessarily a warning sign.
The creatinine elevation from supplementation reflects increased production, not reduced filtration. But the equation that your GP’s blood test relies on cannot tell the difference between the two.
How your blood test interprets this and why it gets it wrong
The standard kidney function test most GPs rely on is called eGFR: estimated glomerular filtration rate. It estimates how quickly your kidneys are filtering your blood, and it uses your serum creatinine level as its primary input.
The equation works on a simple assumption: if creatinine is high in the blood, the kidneys must not be clearing it fast enough, so filtration must be declining.
That assumption holds for most people in most situations. But it has a blind spot: it has no way of knowing why your creatinine is elevated. It just sees the number, assumes the worst, and reports a lower eGFR than your kidneys actually deserve.
A 2025 systematic review and meta-analysis published in BMC Nephrology (literally the most comprehensive analysis of this question to date, covering 21 studies) confirmed that creatine supplementation does produce a small but statistically significant rise in serum creatinine. The rise is most pronounced in the first week of supplementation. This is typically when individuals are supplementing with high loading doses of creatine monohydrate (around 20g/day) to saturate muscle tissue, and this effect flattens out after that, as the meta-analysis showed. Critically, however, the authors concluded that this increase reflects metabolic turnover rather than renal impairment.
The Cleveland Clinic Journal of Medicine made the clinical implications explicit in a 2025 guidance piece: in people taking creatine supplements, creatinine-based eGFR “may not accurately reflect kidney function,” and a dual-marker testing strategy is “strongly recommended.”
Your GP is not wrong to flag it. The test is doing exactly what it was designed to do. The problem is that the standard creatinine-based eGFR was never designed with creatine supplementers in mind.
What the 2025 BMC Nephrology meta-analysis found
21 studies reviewed. Creatine supplementation produces a small, statistically significant rise in serum creatinine, but this rise reflects normal metabolic turnover, not kidney damage. The effect is strongest in the first week of supplementation and does not indicate declining filtration in healthy adults.
What your GP should order instead and how to ask for it
There is a better test for people who take creatine: cystatin C.
Cystatin C is a protein produced at a constant rate by every nucleated cell in the body. Unlike creatinine, it is not influenced by muscle mass, dietary protein intake, or creatine supplementation. This makes it a far more reliable kidney marker for active people, those with higher-than-average muscle mass, and anyone supplementing with creatine.
The evidence for this is now embedded in official clinical guidance. The 2024 KDIGO (Kidney Disease: Improving Global Outcomes) guidelines, the global standard for kidney care, now recommend using both creatinine and cystatin C together for the most accurate assessment of kidney function, particularly in people where body composition or diet may confound creatinine-based results.
In athletes or people using creatine supplements (which can falsely elevate serum creatinine), cystatin C remains unaffected, ensuring a more accurate evaluation.
If your creatinine-based eGFR has declined since starting creatine, but your cystatin C-based eGFR is normal, your kidneys are functioning well. The decline in the creatinine reading is an artefact of the estimation method, not evidence of damage.
How to have the conversation with your GP
You do not need to go in armed with a stack of papers. One sentence is usually enough:
“I’ve been supplementing with creatine monohydrate. I understand this can raise serum creatinine and affect eGFR calculations. Would it be possible to also run a cystatin C test to get a clearer picture of my actual filtration rate?”
We do recognise that this is easier said than done in some cases. Cystatin C may unfortunately not be covered by all insurance plans or readily available at every local clinic at this moment in time. As this article makes clear, the Cystatin C test is not usually the first line of care and investigation. We believe there is an opportunity for patients to increase requests and demand for this type of test, which can create progress and change within the healthcare system.
A few other practical points worth knowing:
Tell your GP before your blood test that you supplement with creatine. Some will note it in your file and interpret results accordingly.
Do not stop supplementing to lower the number before a test without discussing it with your GP. Hiding context does not help either of you.
Avoid taking creatine on the morning of a blood draw; this temporarily spikes levels and adds noise to an already confusing picture.
If your GP is unfamiliar with this distinction, the 2024 KDIGO guidelines and the ISSN 2026 Position Stand on creatine are both freely available and may be useful reference points.
What does the long-term research actually show?
For healthy adults, the evidence base on creatine and kidney health is about as robust as nutrition science gets.
The International Society of Sports Nutrition (ISSN) updated its position on creatine in 2026, reviewing over 680 peer-reviewed clinical trials involving nearly 13,000 participants ranging in age from infants to elderly adults. Their conclusion: no evidence of renal toxicity in healthy individuals at recommended doses (3–5g per day).
A 2024 Mendelian randomisation study (a study design that uses genetic variants to infer causality and eliminate confounding variables) found no statistical association between creatine levels and renal function decline. This is strong evidence that the relationship between creatine supplementation and kidney health is not causal.
The historical case reports that originally seeded concern about creatine and kidneys are worth briefly addressing: the two most-cited cases involved either a pre-existing kidney condition or excessive intake combined with other nephrotoxic substances. They do not represent what happens in healthy individuals using standard supplementation protocols.
One important caveat
People with pre-existing chronic kidney disease (CKD) should work with a healthcare provider and have their labs monitored more carefully before supplementing. There is emerging evidence that people with kidney disease may actually have lower baseline creatine levels and could benefit from supplementation, but this group requires medical supervision, and this article is not a substitute for that conversation.
Getting a worrying blood result is stressful. And a GP advising caution is acting from a place of genuine care; the concern is not unfounded, the test is not broken. It just has a blind spot that most routine blood work has not yet accounted for.
The science is clear: in healthy adults, creatine monohydrate does not damage the kidneys. What it does do is raise serum creatinine levels in a way that confuses a standard eGFR calculation. The fix is not to stop supplementing. The fix is a better test.
If you’ve been told to stop creatine based on a blood result, ask for the full picture before making a decision. Ask for cystatin C. Tell your GP you are supplementing. Don’t make a health decision based on one marker viewed through an incomplete lens.
We all rise together,
Rachael Jennings | Co-Founder + CBO, Jenerise
