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 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.

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).