Is creatine supplementation safe for individuals with a single healthy kidney (unilateral renal function)?

Creatine Safety with a Single Healthy Kidney

Creatine supplementation appears safe for individuals with a single healthy kidney based on direct evidence, but nephrology guidelines specifically discourage its use in this population due to the critical need to preserve remaining renal function. 1

The Evidence Conflict

There is a notable divergence between research findings and nephrology expert consensus:

Research Evidence (Favorable):

• A prospective controlled study in a 20-year-old man with a single kidney showed that high-dose creatine supplementation (20 g/day for 5 days, then 5 g/day for 30 days) did not compromise actual kidney function. 2
• Measured GFR by 51Cr-EDTA clearance remained unchanged (81.6 vs 82.0 mL/min/1.73 m²) despite serum creatinine rising from 1.03 to 1.27 mg/dL. 1, 2
• Multiple systematic reviews conclude that creatine supplementation does not cause kidney dysfunction in healthy individuals, even with long-term use (up to 5 years). 3, 4, 5

Guideline Position (Cautious):

• The American Journal of Kidney Diseases explicitly discourages creatine supplementation in kidney donors and individuals with solitary kidneys due to compromised renal reserve. 6
• The rationale is that any substance with uncertain long-term effects should be avoided when renal reserve is already reduced by 50%. 1
• This represents a precautionary principle rather than evidence of harm. 6

My Recommendation

For individuals with a single healthy kidney (normal GFR, no proteinuria, no other risk factors), I recommend against routine creatine supplementation, prioritizing the nephrology consensus that emphasizes preservation of remaining kidney function over ergogenic benefits. 6

Decision Algorithm:

If you choose to proceed despite guideline recommendations:

1. Baseline Assessment Required: 6

   • Measure actual GFR using cystatin C or measured GFR (not creatinine-based eGFR, which creatine will falsely lower) 6
   • Check spot urine albumin-to-creatinine ratio to ensure no baseline kidney damage 6
   • Verify blood pressure is well-controlled (<130/80 mmHg) 1

2. Absolute Contraindications: 6, 7, 5

   • GFR <45 mL/min/1.73 m²
   • Any degree of proteinuria or albuminuria
   • Diabetes, hypertension, or other kidney disease risk factors
   • Concurrent use of nephrotoxic medications (NSAIDs, certain antibiotics)

3. If Proceeding (GFR ≥60 mL/min/1.73 m², no proteinuria): 2, 4

   • Use standard maintenance dose only (3-5 g/day), avoid loading phases
   • Monitor with cystatin C-based GFR every 3-6 months (not creatinine-based eGFR) 6
   • Check urine albumin-to-creatinine ratio every 6 months 6
   • Discontinue immediately if any albuminuria develops

Critical Pitfalls to Avoid

Do not use serum creatinine or creatinine-based eGFR to monitor kidney function during creatine supplementation. 1, 6, 2

• Creatine supplementation increases serum creatinine by 0.2-0.3 mg/dL through non-pathologic conversion to creatinine, falsely suggesting kidney dysfunction. 1, 2
• This creates diagnostic confusion and can lead to misdiagnosis of chronic kidney disease when none exists. 6
• Use cystatin C, measured GFR, or urine albumin-to-creatinine ratio instead. 6

Do not assume short-term safety equals long-term safety. 1

• The single-kidney study was only 35 days in duration. 2
• No long-term (>1 year) controlled studies exist specifically in single-kidney populations. 3, 4
• The nephrology community's caution reflects this evidence gap. 6

Do not combine creatine with other nephrotoxic exposures. 7, 5

• Avoid NSAIDs, high-dose protein (>1.3 g/kg/day), and dehydration. 6, 5
• These combinations may unmask subclinical kidney stress that a solitary kidney cannot compensate for. 5

The Bottom Line

While research evidence suggests creatine does not directly damage kidneys, the nephrology consensus prioritizes maximal preservation of the single remaining kidney over potential performance benefits. 6 Given that individuals with one kidney have 50% reduced renal reserve and no backup if that kidney fails, the risk-benefit calculation differs fundamentally from two-kidney populations. 1 I align with the guideline recommendation to avoid creatine in this population. 6