What kidney function markers, aside from serum creatinine, should be assessed to evaluate renal function in individuals taking creatine (creatine monohydrate)?

From the Guidelines

To adequately assess kidney function while taking creatine supplements, you should monitor several markers beyond serum creatinine, including blood urea nitrogen (BUN), estimated glomerular filtration rate (eGFR), cystatin C, and urinalysis parameters. These markers are more reliable indicators of kidney function, especially since creatine supplementation can artificially elevate creatinine levels without actual kidney damage, as noted in the context of evaluating kidney function 1. Cystatin C is particularly valuable as it remains unaffected by creatine intake, and its measurement is suggested in specific clinical scenarios to confirm chronic kidney disease (CKD) 1. A comprehensive metabolic panel that includes electrolytes (sodium, potassium, calcium, phosphorus) can also provide insights into kidney function. Consider requesting these tests every 3-6 months if you're taking creatine regularly, or more frequently if you have pre-existing kidney concerns. Staying well-hydrated (about 3-4 liters of water daily) while taking creatine (typically 3-5g daily) is important for kidney health. The artificial elevation in creatinine occurs because creatine is metabolized to creatinine in the body, increasing blood levels without necessarily indicating kidney dysfunction. This is why multiple markers provide a more accurate picture of your actual kidney function during creatine supplementation. Key points to consider include:

• Monitoring BUN, eGFR, cystatin C, and urinalysis parameters in addition to serum creatinine.
• The importance of cystatin C in confirming CKD, especially when eGFR based on creatinine is between 45-59 ml/min/1.73 m^2 1.
• Regular hydration and consideration of electrolyte balance.
• The need for periodic assessment of kidney function tests, tailored to the individual's health status and creatine supplementation regimen.

From the Research

Kidney-Related Markers for Assessing Kidney Function

To adequately assess kidney function, especially when taking creatine supplements, the following markers should be considered:

• Serum creatinine: Although creatine supplements may transiently rise serum creatinine levels, it is still an essential marker for kidney function 2.
• Blood urea nitrogen (BUN): Elevated BUN levels can increase confusion when assessing kidney function, especially if combined with a high protein diet 2.
• Cystatin C: This marker can be used as an alternative to serum creatinine, especially in cases where creatinine-based estimated glomerular filtration rate (eGFR) may be invalid 3, 4.
• Glomerular filtration rate (GFR): Measuring GFR using an exogenous marker such as iohexol can provide a more accurate assessment of kidney function, especially in clinical scenarios where creatinine-based eGFR may be limited 3.
• Plasma and urinary sodium and potassium: These markers can help assess renal function, particularly in healthy individuals undergoing exercise training 4.
• Plasma albumin clearance: This marker can help evaluate glomerular membrane permeability and tubular reabsorption 5.

Clinical Scenarios for Alternative Markers

Alternative markers such as cystatin C and measured GFR may be necessary in certain clinical scenarios, including:

• Extreme body composition
• Black race
• Disagreement between creatinine- and cystatin C-based eGFR
• Drug dosing
• Liver cirrhosis
• Advanced chronic kidney disease
• Non-kidney solid organ transplant recipients
• Living kidney donors 3

Safety of Creatine Supplementation

Studies have consistently shown that creatine supplementation does not cause renal damage or impair kidney function in healthy individuals 4, 6, 5. However, it is essential to note that creatine supplements should not be used in people with chronic renal disease or those using potentially nephrotoxic medications 2.