Can creatine supplementation cause an estimated Glomerular Filtration Rate (eGFR) of 55 mL/min per 1.73 square meters, indicating Impaired Renal Function?

Creatine Supplementation Can Cause Falsely Elevated Serum Creatinine and Decreased eGFR Without Actual Kidney Dysfunction

Yes, the reduced eGFR of 55 mL/min per 1.73m² is very likely due to creatine supplementation rather than true kidney dysfunction. Creatine supplements can artificially elevate serum creatinine levels, leading to a falsely decreased eGFR calculation without actual impairment of kidney function.

How Creatine Affects Laboratory Values

• Creatine is an amino acid that is spontaneously converted to creatinine in the body 1
• Supplementation increases the creatinine pool, resulting in higher serum creatinine levels
• Since eGFR calculations (like the MDRD equation) use serum creatinine as a key variable, elevated creatinine from supplements falsely suggests reduced kidney function 2
• This is a well-documented phenomenon that can lead to unnecessary concern about kidney disease

Evidence Supporting This Effect

• Case reports have consistently shown that creatine supplementation can transiently increase serum creatinine while actual kidney function remains normal 2, 3
• In a controlled study of a young man with a single kidney, creatine supplementation increased serum creatinine from 1.03 mg/dL to 1.27 mg/dL and decreased estimated creatinine clearance, but had no effect on actual measured GFR using gold standard methods 4
• The 2023 review in Nutrients confirms that despite elevated creatinine levels in some individuals taking creatine supplements, studies using reliable kidney function assessment methods show no actual kidney dysfunction 1

Interpretation of Your Laboratory Results

Your laboratory values show:

• Elevated serum creatinine: 121 μmol/L (reference range: 60-110)
• Reduced eGFR: 55 mL/min per 1.73m² (reference: >60)
• Normal urea: 6.4 mmol/L (reference range: 3.0-10.0)
• Normal potassium: 5.1 mmol/L (reference range: 3.5-5.2)

The pattern of isolated creatinine elevation with normal urea and electrolytes is consistent with creatine supplementation rather than true kidney disease.

Recommendations for Accurate Assessment

1. Discontinue creatine supplementation for at least 4-6 weeks before retesting kidney function 2

2. Consider alternative GFR assessment methods if clinical decision-making is urgent:

   • Cystatin C-based eGFR (eGFRcys) which is not affected by creatine supplementation 5
   • Measured GFR using exogenous filtration markers (gold standard) 6
   • 24-hour urine collection for measured creatinine clearance 5

3. Monitor for true signs of kidney dysfunction which would include:

   • Albuminuria/proteinuria
   • Electrolyte abnormalities
   • Elevated blood urea nitrogen disproportionate to creatinine
   • Hypertension
   • Edema

Important Caveats

• While creatine supplementation can cause laboratory abnormalities, it is generally considered safe for individuals with normal kidney function 7
• Creatine supplements should be avoided in people with established chronic kidney disease or those taking potentially nephrotoxic medications 7
• KDIGO guidelines recommend assessing the potential for error in eGFR when evaluating changes in GFR over time, particularly when non-GFR determinants like creatine supplementation may be present 5

If you need to make clinical decisions based on accurate kidney function assessment while continuing creatine supplementation, consider using cystatin C-based eGFR or measured GFR methods that are not influenced by creatine intake.