Taking Creatine? Why Your Creatinine Test Can Change
Picture opening a routine blood report a few months after you started taking creatine. Creatinine is flagged high. A few rows down, eGFR is flagged low. It looks like two tests delivering the same bad news.
Before you worry about two problems, check where that second number came from.
Two similar names, different jobs
Creatine helps muscles supply energy for short, hard efforts. Your body makes it, and you get some from food. As creatine is used and broken down, some of it becomes creatinine, a waste product your kidneys clear from the blood. The NIH fact sheet on creatine explains how the two nearly identical names are connected.
Think of blood creatinine like the water level in a bathtub with the tap on and the drain open. The level depends on both. A slower drain (less filtering) raises it. So does opening the tap wider (making more creatinine). The analogy has limits, since your body isn't a tub, but it shows why one number can't tell you which side changed.
Creatine use can open the tap wider by adding to the supply of this waste product. That's why kidney-test guidance lists creatine supplements among the things that can raise creatinine, alongside high muscle mass, recent hard exercise and eating cooked meat.
None of that makes the test meaningless. It means the number needs context the report doesn't show.
The "e" in eGFR matters
GFR stands for glomerular filtration rate: how quickly your kidneys filter blood. The e means estimated. A common adult equation takes your blood creatinine, age and sex and calculates the estimate. Nobody watches your kidney filters at work. NIDDK shows what goes into the calculation.
With age and sex unchanged, higher creatinine gives a lower creatinine-based eGFR. So those two flagged rows may be one measurement and a calculation made from it. It's one warning light wired to a second bulb.
Here's a hypothetical example. Compare two reports from the same adult, one before starting creatine and one after. The later report shows higher creatinine and lower eGFR. Those two changes fit together through the equation. What they can't tell you, on their own, is whether more creatinine was being made, less was being cleared, or both.
What happened when studies measured filtering directly?
A 2026 review of 26 randomized trials with 1,036 participants compared the two kinds of evidence. Groups taking creatine had higher creatinine and lower creatinine-based filtration results. But in trials that measured filtering with a tracer method called Cr-EDTA, which doesn't rely on creatinine, there was no statistically significant difference between the groups.
Together, those findings support the idea that creatine can move the marker without a matching change in filtering. A lack of a statistically significant difference doesn't prove harm is impossible, and the studies can't explain any one person's result.
The gaps are worth knowing too. The review found no trials in people with chronic kidney disease who weren't on dialysis, only four trials that lasted longer than six months, and only two that checked cystatin C, another filtration marker. So this is reassuring evidence about the test, not a safety guarantee for everyone.
A second marker can help
Cystatin C is a protein made by cells throughout the body, and it can also be used to estimate filtering. Because it doesn't come from creatine, clinicians sometimes use it when a creatinine result is unclear or when muscle mass makes it hard to interpret. The cystatin C guidance explains when it's used.
It has its own blind spots: untreated thyroid conditions and steroid medicines can throw it off. An estimate that combines creatinine and cystatin C is generally more accurate than creatinine alone, though when something strongly affects either marker, choosing the right equation takes individual judgment. NIDDK describes that exception.
A good question to bring: "Could a cystatin C test help interpret this result?"
A urine test asks a different question
Blood tests estimate how fast your kidneys filter. A urine albumin test asks something else: whether a blood protein is leaking through damaged filters. NIDDK explains why the two tests complement each other.
You may see it reported as uACR, the urine albumin-to-creatinine ratio. Yes, creatinine shows up again, but here it's measured in urine to account for how concentrated the sample is. It isn't a repeat of the blood result. The uACR guide explains the ratio.
Albumin can leak even when eGFR is normal, and a normal urine result doesn't rule out every kidney problem. An abnormal uACR may need repeating, because recent hard exercise or an infection can raise it for a while. Follow your care team's collection instructions.
Another good question: "Has my urine albumin been checked, and would it add anything here?"
Bring a timeline, not a theory to defend
Before your follow-up, put the earlier and current reports next to your supplement label. Note when you started creatine or switched products, and write down exactly what you take, not just "sports supplements." Creatine monohydrate is the most studied form; a blend with several ingredients isn't automatically the same thing the trials tested. NIH discusses the limits of applying single-ingredient research to blends.
Also mention any recent illness, symptoms and every medicine you take, including over-the-counter products and herbs. Clinicians use those details when assessing a sudden kidney change. Don't stop prescribed medicines on your own, and don't pick your own supplement break before a repeat test. Ask the team that ordered it how to prepare.
If the flags on your report are confusing, here's how to read high and low blood-test flags. And our doctor visit checklist can help turn your timeline into a short note.
Want to talk through your own report first? Ask the free SageWiz health chat, for example: "I take creatine and my creatinine went up. What should I ask about how my kidney function was checked?" The chat is educational and for adults 18 and over in the US.
Caveats
Feeling fine doesn't settle a changed result, because early kidney disease often causes no symptoms. Diabetes, high blood pressure, heart disease and a family history of kidney failure also matter when a result is assessed. NIDDK outlines those risks.
This article explains adult lab tests. It isn't a recommendation to start or keep taking creatine if you have kidney disease. Your supplement history helps interpret a result; it doesn't outweigh the rest of your medical picture.
So next time those two rows are flagged together, ask which number was measured, which was calculated from it, and what test would add genuinely new information. That's a clearer place to start than counting flags.
Curious how we research and check our articles? Read How SageWiz Researches and Checks Its Health Articles.
Evidence
The 2026 review pooled randomized trials, mostly in healthy adults, to see what happened to kidney tests in groups taking creatine; its long-term data are limited and it included no trials in people with non-dialysis kidney disease. The National Kidney Foundation and NIH guidance explain what each measurement means and what can affect it. None of these sources can identify the cause of your own result. The NIDDK patient page was last reviewed in October 2016; current professional guidance supplies the equation details.
Evidence used in this article
Primary sources and public health references reviewed for this article.
- Impact of creatine supplementation on kidney health: a systematic review and meta-analysis
systematic review/meta-analysis of randomized trials
Review of 26 randomized trials; creatinine-based results differed from Cr-EDTA measured filtration. Limited long-term data and no non-dialysis CKD trials.
- Creatinine
National Kidney Foundation patient guidance
Explains creatinine, non-kidney influences and test preparation.
- Cystatin C
National Kidney Foundation patient guidance
When cystatin C can help and what can affect its accuracy.
- Chronic Kidney Disease Tests & Diagnosis
NIH/NIDDK patient guidance
Complementary blood and urine testing; early disease may lack symptoms. Last reviewed October 2016.
- Dietary Supplements for Exercise and Athletic Performance
NIH Office of Dietary Supplements health-professional fact sheet
Creatine metabolism, studied forms and limits of multi-ingredient products.
- Acute Kidney Injury (AKI)
National Kidney Foundation patient guidance
Sudden kidney changes, assessment and urgent warning signs.
- Urine albumin-creatinine ratio (uACR)
National Kidney Foundation patient guidance
Urine albumin relative to urine creatinine, sample factors and confirmation.
- eGFR Equations for Adults
NIH/NIDDK professional laboratory guidance
Adult filtration equations, combined-marker accuracy and individual exceptions.
