Creatine is a compound found naturally in muscle cells and is widely used as a dietary supplement to enhance athletic performance and increase muscle mass. The body naturally produces creatine, which is also obtained through the diet, primarily from meat and fish. Individuals who supplement with creatine often worry that it might interfere with routine medical blood tests, potentially leading to misinterpretation of results. This article explores the biological reasons for this concern and provides guidance on preparing for a blood test while using creatine.
Blood Markers Affected by Creatine
Creatine supplementation directly impacts serum creatinine levels, the primary blood marker affected on a standard metabolic panel. Creatinine is a waste product constantly produced and released into the bloodstream, where it is filtered out by the kidneys. When creatine supplements are taken, the amount of creatine stored in the muscles increases, elevating the total amount of creatinine produced.
This increase in serum creatinine, while not indicative of actual kidney damage, can lead to a calculated reduction in the estimated Glomerular Filtration Rate (eGFR). The eGFR calculation uses the serum creatinine level, along with age, sex, and sometimes race, to estimate how well the kidneys are filtering waste. The elevated creatinine level artificially lowers the calculated eGFR, which can falsely suggest impaired kidney function. Creatine supplementation does not significantly affect the Blood Urea Nitrogen (BUN) level, which is another common marker used to assess kidney health.
The Conversion of Creatine to Creatinine
The elevation of serum creatinine is due to the natural metabolic process of creatine within the body. Creatine is primarily stored in muscle tissue as phosphocreatine, an energy reserve used to quickly regenerate adenosine triphosphate (ATP) during intense exercise. Through a non-enzymatic reaction, creatine and phosphocreatine are constantly broken down into creatinine.
Creatinine is a waste product that must be excreted, as it cannot be recycled or used for energy. The conversion rate depends largely on the total amount of creatine stored in the muscle mass. Introducing supplemental creatine increases the total creatine pool, which directly leads to increased production and circulation of the creatinine waste product observed in blood tests.
Why Doctors Care About Creatinine Levels
Creatinine is widely used in clinical settings as a proxy measure for kidney function. The kidneys filter creatinine from the blood and excrete it in the urine, making its concentration a good indicator of filtering efficiency. When kidney function declines, the kidneys are less efficient at clearing this waste product, causing the serum creatinine level to rise.
An elevated creatinine level without context is a major red flag for physicians, suggesting the possibility of acute or chronic kidney disease. A low eGFR is automatically calculated from this elevated creatinine, often prompting further diagnostic testing. Since the rise in creatinine from supplementation is due to increased production and not actual kidney impairment, the test result creates a “false positive” or pseudo-renal failure.
Recommended Protocol Before Testing
Health professionals generally agree that individuals taking creatine should temporarily stop before a blood test to ensure accurate interpretation of kidney function. This allows elevated creatinine levels to return to a natural baseline. This brief interruption, often called a “washout period,” is recommended to last between three and seven days prior to the blood draw.
Some sources suggest a longer period of one to two weeks, especially for individuals who have fully saturated their muscle stores. Regardless of whether supplementation is stopped, it is important to inform the physician or lab technician about all supplements being taken, including creatine. This disclosure allows the medical team to interpret an elevated creatinine result correctly, preventing potential misdiagnosis or unnecessary follow-up tests.