Should I obtain a baseline serum creatinine and estimated glomerular filtration rate (eGFR) before starting creatine supplementation?

Should You Get Your eGFR/Cr Before Starting Creatine?

No, obtaining baseline serum creatinine and eGFR before starting creatine supplementation is not medically necessary for healthy individuals, but it is prudent if you have pre-existing kidney disease, use nephrotoxic medications, or will need accurate kidney function assessment for other medical purposes while taking creatine.

Why Baseline Testing Is Generally Not Required

• Creatine supplements are safe and do not cause kidney disease in healthy individuals, with reports of kidney damage associated with creatine use being extremely rare 1
• The primary concern with creatine supplementation is not actual kidney damage, but rather artifactual elevation of serum creatinine that can falsely suggest kidney disease when none exists 1, 2
• Creatine supplements transiently raise serum creatinine levels because creatine is converted to creatinine in muscle tissue, increasing the measured serum creatinine without any actual decline in kidney function 1, 2

The Real Problem: Misdiagnosis, Not Kidney Damage

• When laboratories automatically calculate eGFR based on elevated serum creatinine from creatine supplementation, this can lead to over-diagnosis of chronic kidney disease with significant personal and public health consequences 1
• A 54-year-old woman was unnecessarily referred to nephrology for "impaired renal function" based solely on eGFR calculated during creatine supplementation; her kidney function normalized completely after stopping creatine 2
• Serum creatinine alone is inadequate for GFR assessment because it reflects not only kidney excretion but also creatinine generation, intake, and metabolism 3, 4

When Baseline Testing IS Recommended

You should obtain baseline creatinine/eGFR before starting creatine if:

• You have known chronic kidney disease - Creatine supplements should not be used in people with pre-existing chronic renal disease 1
• You take potentially nephrotoxic medications - Baseline kidney function assessment is essential before initiating drugs with nephrotoxic potential, and creatine should be avoided in this context 5, 1
• You need accurate kidney function monitoring for other medical conditions - If you require precise GFR assessment for medication dosing (especially chemotherapy or other narrow therapeutic window drugs) or disease monitoring, baseline testing allows comparison 6, 4
• You have risk factors for kidney disease - Black patients, those with diabetes, hypertension, or advanced HIV disease have increased nephropathy risk and warrant baseline assessment 5

Practical Algorithm for Creatine Users

For Healthy Individuals Without Kidney Disease:

1. No baseline testing required - You can start creatine supplementation without obtaining creatinine/eGFR 1
2. Inform healthcare providers - Always disclose creatine use when having blood work done, as this prevents misinterpretation of elevated creatinine 2
3. Temporarily discontinue before testing - If kidney function assessment is needed for medical purposes, stop creatine for 2-4 weeks before testing to obtain accurate baseline values 1, 2

For Individuals With Kidney Disease or Risk Factors:

1. Obtain baseline creatinine and eGFR using the 2021 CKD-EPI equation 7, 5
2. Consider cystatin C measurement if you have extremes of muscle mass or body composition, as creatine supplementation combined with altered muscle mass makes creatinine-based eGFR particularly unreliable 4, 7
3. Do not start creatine if you have chronic kidney disease or use nephrotoxic medications 1

Critical Caveats

• High protein diets combined with creatine create additional confusion, as the resulting increase in blood urea nitrogen (BUN) compounds the false appearance of kidney disease 1
• 24-hour urine creatinine clearance may be useful for individuals using creatine supplements who need accurate GFR assessment, as this is specifically recommended for those with exceptional dietary intake including creatine supplementation 8
• Serum creatinine reflects muscle mass - The use of creatine-containing supplements influences serum creatinine levels and therefore the eGFR calculated with standard formulas, independent of actual kidney function 2, 4
• Clinical context is essential - Never rely solely on eGFR thresholds; consider clinical context, rate of change, and presence of other kidney damage markers (such as albuminuria) when interpreting kidney function in creatine users 9, 5

What to Monitor Instead

• Rather than routine creatinine/eGFR monitoring, watch for actual symptoms of kidney disease: changes in urine output, edema, unexplained fatigue, or uremic symptoms 5
• If kidney function testing becomes necessary while taking creatine, measure urine albumin-to-creatinine ratio (ACR) - albuminuria indicates true kidney damage and is not affected by creatine supplementation 9
• Consider cystatin C-based eGFR if precise kidney function assessment is needed while continuing creatine, as cystatin C is less influenced by muscle mass and dietary factors than creatinine 4, 7