Does creatine affect blood test results?
The short answer
Yes. Creatine supplements can raise your serum creatinine slightly, which can make a creatinine-based eGFR look lower even when your kidneys are working normally. Cystatin C is a kidney marker that is not affected by creatine in the same way.
What to do
- Tell your clinician that you take creatine, and how much, before they read your kidney results.
- Keep your routine the same between tests so results compare like with like.
- If your creatinine or eGFR is borderline, ask about adding a cystatin C test.
- Follow your test's fasting rules: the CMP and BMP ask for an 8-hour fast; the kidney panel and cystatin C do not need fasting.
- If you have known kidney disease, ask your clinician before you use creatine.
Which results it changes
| Marker | Effect | How long |
|---|---|---|
| Creatinine[1][2] | Can rise slightly while you take creatine | While supplementing; how fast it returns to baseline is not well studied |
| eGFR (creatinine-based)[3] | Can read lower than your true kidney function | While creatinine is raised |
| Cystatin C / eGFR (cystatin C-based)[3][4] | Not changed by creatine in the reports reviewed | Not applicable |
| Kidney filtration (GFR)[1] | No significant change in pooled studies | Not applicable |
Why creatine shows up as creatinine
Your body converts creatine into creatinine on its own, and your kidneys clear the creatinine from your blood. Creatinine is the kidney marker in the CMP, the BMP and the kidney panel, and eGFR (estimated glomerular filtration rate) is calculated from it.
When you take a creatine supplement, there is more creatine to turn into creatinine. A 2025 meta-analysis of 12 studies found a small but statistically significant rise in serum creatinine with creatine use, with no significant change in kidney filtration (GFR).
Higher creatinine is not the same as kidney damage
A narrative review of the research concluded that controlled clinical trials do not support the idea that creatine harms the kidneys in healthy people. Creatine may raise creatinine for some people, but that rise does not by itself mean the kidneys are working less well.
In a 3-month randomized trial, healthy men took about 10 g of creatine a day while training. Their cystatin C, a kidney marker that does not come from creatine, did not show any kidney dysfunction. The same review notes that more research is needed in people who already have kidney disease.
What it does to your eGFR
The standard eGFR formula assumes your creatinine level mainly reflects how well your kidneys filter. Creatine supplements, a high-protein diet and high muscle mass can all push creatinine up and make a creatinine-based eGFR read lower than your true kidney function.
Doctors have described patients who were labeled with chronic kidney disease from creatinine alone, until a cystatin C-based eGFR showed their kidneys were fine.
Cystatin C as a second look
Cystatin C is a different marker your kidneys filter. In the reports above, creatine lowered the creatinine-based eGFR but did not change the cystatin C-based eGFR.
The 2024 KDIGO kidney guideline recommends equations that combine creatinine and cystatin C to diagnose and stage chronic kidney disease. Reviews also note that cystatin C can improve kidney estimates in people whose muscle mass is changing. JustLabs offers a cystatin C test you can order alongside a kidney panel, CMP or BMP.
Should you stop creatine before a test?
We did not find a study that sets a standard creatine break before a blood test. The research shows that creatinine rises, but it does not pin down how long it takes to come back down after you stop.
So there is no evidence-based number of days to quote. The practical approach is to tell your clinician you take creatine, keep your routine steady between tests, and ask whether a cystatin C test or a repeat test fits your situation.
Frequently Asked Questions
More on preparing
Sources
- Naeini EK, Eskandari M, Mortazavi M, Gholaminejad A, Karevan N. Effect of creatine supplementation on kidney function: a systematic review and meta-analysis. BMC Nephrol. 2025 Nov 6;26(1):622. doi: 10.1186/s12882-025-04558-6. PMID: 41199218. PubMed
- Longobardi I, Gualano B, Seguro AC, Roschel H. Is It Time for a Requiem for Creatine Supplementation-Induced Kidney Failure? A Narrative Review. Nutrients. 2023 Mar 18;15(6). doi: 10.3390/nu15061466. PMID: 36986197. PubMed
- Beckstead A, Holmes HR, Tran V, Dass B. My Kidney Is Fine, Can't You Cystatin C?. Fed Pract. 2024 Feb;41(2):62-66. doi: 10.12788/fp.0440. PMID: 38835922. PubMed
- Gualano B, Ugrinowitsch C, Novaes RB, Artioli GG, Shimizu MH, Seguro AC, Harris RC, Lancha AH Jr. Effects of creatine supplementation on renal function: a randomized, double-blind, placebo-controlled clinical trial. Eur J Appl Physiol. 2008 May;103(1):33-40. doi: 10.1007/s00421-007-0669-3. PMID: 18188581. PubMed
- Awdishu L, Karger AB, Shlipak MG, Estrella MM. Use of Cystatin C in Tandem with Creatinine to Improve GFR Estimation and Clinical Decision Making. J Am Soc Nephrol. 2026 Sep 1;37(9):2042-2054. doi: 10.1681/ASN.0000001201. PMID: 42424121. PubMed
Content reviewed for accuracy by the JustLabs editorial team.
Educational information, not medical advice. Don’t stop or change a prescribed medicine without talking to your prescriber. If your lab order gives different instructions, follow your lab order.