Does taking creatine affect blood or urine test results?

Answer:

Supplementing with creatine may cause small, temporary increases in creatinine levels (a measure of kidney function), but it does not appear to affect kidney function itself, nor more reliable measures of kidney health, such as glomerular filtration rate (GFR) and blood urea levels (Tsiaras, J Ren Nutr 2026; Naeini, BMC Nephrol 2025; Williamson, BMJ Case Rep 2014; Poortmans, Med Sci Sports Exerc 1999). Creatine supplementation also does not affect creatine kinase (CK) activity (a measure of muscle breakdown) in most people (Persky, Creatine and Creatine Kinase in Health and Disease 2007). Many experts consider the risk of kidney injury due to short-term creatine supplementation to be low even among people with pre-existing kidney dysfunction (Kreider, J Int. Soc Sports Nutr 2017), although the long-term safety among these individuals remains unclear.

To be safe, if you have pre-existing kidney dysfunction or take high doses of creatine, particularly the ethyl ester form, consult with your healthcare provider before taking creatine. Also, let your physician know in advance, and/or stop supplementation two weeks before getting a blood test that measures creatinine for kidney function. Also be aware that a blood tests for cystatin C (a protein that can be elevated in people with reduced kidney function), instead of or in addition to a blood creatinine test, can also be useful and more accurate in determining kidney function (including estimated glomerular filtration rate, or eGFR) than testing for creatinine alone in some people, as cystatin C levels are less affected by age, gender, and muscle size (Osredkar, Int J Mol Sci 2025; American Kidney Fund 2025).

For details, see the Concerns and Cautions section of the Muscle & Workout Supplements Review, which includes ConsumerLab.com's tests of popular products and our Top Picks for creatine and BCAAs (branched-chain amino acids).