This is a question asked during consultations more often than one might imagine, and one that brands almost never answer: creatine changes blood test results. Not because it damages anything, but because it interferes with the way kidney function is measured.
In summary. Creatine slightly increases blood creatinine, the marker used to estimate kidney function. This rise reflects supplementation, not kidney impairment. Mention it at the time of the blood draw: this is what avoids a false alarm, a follow-up, and sometimes an unnecessary examination.
Creatine and creatinine: two words, two things
The confusion stems first from the names.
Creatine is the molecule stored by muscles, and the one you take as a supplement. Creatinine is its breakdown product: muscles spontaneously convert about 1 to 2% of it daily, and the kidneys eliminate it in urine.
It is this waste product, and not the creatine itself, that the laboratory measures. Since it is eliminated exclusively by the kidneys, its blood concentration serves as an indicator of the organ's proper functioning.
The logic can therefore be summarized in one sentence: the more creatine there is in the muscle, the more creatinine is produced, and the higher the measured level — without the kidneys having changed their workload in any way.
The number goes up because there is more material to eliminate, not because the filter is working less efficiently.
Why it can trigger a false alarm
The laboratory does not just report the creatinine level: it uses it to calculate an estimated glomerular filtration rate, or eGFR. This is the figure that appears on the report and is used to classify kidney function.
However, this calculation is based on an assumption: that creatinine comes solely from ordinary muscle metabolism. Under supplementation, the assumption no longer holds. The estimated GFR drops mechanically, without any decrease in actual filtration.
The same bias exists in very muscular people, and conversely in elderly people with low muscle mass, in whom the GFR is overestimated. This is not a flaw in the test — it is a known limitation of the method, which context allows one to correct.
What to do, in practical terms
Mention it. When the prescription is written if you think of it, otherwise at the laboratory, or when reading the results. One line is enough: "I have been taking 5g of creatine monohydrate per day for X months." This is the information the doctor needs to interpret the results correctly.
Do not stop on your own before the analysis. Unless explicitly requested by your doctor. Stopping a few days before skews the reading in the other direction and removes the very context that is useful.
Avoid intense exertion the day before. A strength training session or a long run temporarily elevates creatinine, regardless of any supplementation. This is a classic recommendation before a kidney check-up.
Stay normally hydrated. Dehydration concentrates blood parameters and adds a bias.
If the result is worrying despite everything
There are ways to settle the matter, and it is up to the doctor to decide which ones.
Cystatin C is another marker of kidney function that is independent of muscle mass and therefore not influenced by creatine. It is increasingly used precisely in situations where the estimation by creatinine is found to be flawed.
A follow-up after a few weeks of stopping, based on medical advice, also allows for comparison.
In any case, a single number does not make a diagnosis. It must be interpreted alongside urine analysis, medical history, and context.
What it does not mean
This increase is not a sign of kidney damage. In people with healthy kidneys at standard doses, more than thirty years of studies have not shown any harm2.
It also does not mean that creatine "strains" the kidneys: there is no overload, only more material to be eliminated by a mechanism that is functioning normally.
And it is not a reason to stop. It is a reason to mention it.
When the question really is one for a doctor
If you have a known kidney condition, or a history that justifies monitoring, the decision to take creatine should be made with them — before starting, not at the time of the check-up.
The same applies in the case of long-term treatment, particularly for those requiring renal monitoring.
Aplomb is creatine monohydrate in 5g single-dose sticks. One active ingredient, one pre-measured dose, nothing else.
To learn more: the 19 most frequently asked questions · creatine for women · creatine and menopause
References
- Smith-Ryan AE, Cabre HE, Eckerson JM, Candow DG. Creatine Supplementation in Women's Health: A Lifespan Perspective. Nutrients 2021;13(3):877.
- Kreider RB et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. J Int Soc Sports Nutr 2017;14:18.
- Antonio J et al. Common questions and misconceptions about creatine supplementation: what does the scientific evidence really show? J Int Soc Sports Nutr 2021;18:13.
Article written by Virginie Mauran. This information is general and does not replace individual medical advice.