Creatine and Kidney Disease Medications: How to Monitor Renal Function Safely

When you take creatine, your body turns it into creatinine - a waste product your kidneys filter out. That’s fine if your kidneys are healthy. But if you’re on kidney disease medications like ACE inhibitors, diuretics, or NSAIDs, that simple conversion can mess with your lab results in ways doctors might not expect. You could walk away from a routine blood test thinking you have kidney damage - when you don’t. And that’s not just a scare. It can lead to unnecessary tests, anxiety, and even changes in your treatment plan.

Why Creatine Throws Off Kidney Lab Tests

Creatine monohydrate, the most common form, gets absorbed by your muscles and then slowly breaks down into creatinine. That creatinine shows up in your blood. And here’s the problem: doctors use that number - serum creatinine - to calculate your eGFR, which tells them how well your kidneys are filtering. A normal eGFR is above 90. Below 60 for three months means chronic kidney disease.

But creatine raises serum creatinine by 10% to 30% in healthy people. That’s not because your kidneys are failing. It’s because you’re dumping more creatinine into your system. A 2020 study in the Clinical Journal of the American Society of Nephrology found that creatine users with perfectly normal kidney function often had eGFR readings that looked like stage 2 kidney disease. When they stopped taking creatine, their eGFR jumped back up - not because their kidneys got better, but because the creatinine dropped.

One Reddit user, a fitness student, got flagged for stage 2 CKD (eGFR 78) while taking 5 grams a day. He didn’t have symptoms. No swelling. No fatigue. His doctor ordered more tests. He stopped creatine for two weeks. His eGFR went to 95. No kidney damage. Just a misleading number.

What Happens When Creatine Meets Kidney Medications

If you’re on medication for kidney disease, your kidneys are already working harder. Some drugs - like NSAIDs (ibuprofen, naproxen), ACE inhibitors (lisinopril), or ARBs (losartan) - help protect your kidneys by lowering blood pressure and reducing protein loss. But they also change how your body handles waste.

Creatine adds extra creatinine into the mix. That’s not dangerous by itself. But when your kidneys are already compromised, that extra load can make it harder to tell what’s going on. Are your creatinine levels high because of the creatine? Or because your kidney disease is getting worse? The two look identical on a lab report.

There’s no evidence that creatine causes kidney damage in healthy people. A 2024 Mendelian randomization study in Renal Failure looked at genetic data from thousands of people and found no link between creatine levels and kidney function. But for someone with existing kidney disease? The risk isn’t about creatine causing harm - it’s about creatine hiding harm.

Case reports exist where people with no prior kidney issues developed acute tubular necrosis while taking 3 grams a day. But these are rare. One in thousands. The bigger issue? Doctors don’t always ask about supplements. A 2021 study in American Family Physician found 67% of primary care doctors never ask patients if they’re taking creatine - even when creatinine is high.

How to Know If Your Kidneys Are Really Failing

Don’t rely on serum creatinine alone if you’re taking creatine. That number is broken for you. You need better tools.

• Cystatin C - This is your best friend. Unlike creatinine, cystatin C isn’t affected by creatine supplements. It’s a more accurate marker of kidney filtration. The CKD-EPI equation using cystatin C gives you a true eGFR. If your cystatin C-based eGFR is normal, your kidneys are fine - even if your creatinine is sky-high.
• 24-hour urine creatinine clearance - This measures how much creatinine your kidneys actually clear out over a full day. If your urine creatinine output stays steady while your blood creatinine rises, it’s the supplement, not your kidneys.
• Blood urea nitrogen (BUN) - Creatine doesn’t raise BUN. If your BUN is high along with creatinine, that’s a red flag. It suggests real kidney trouble.
• Urine protein - Healthy kidneys don’t leak protein. If your urine shows protein (proteinuria), that’s a sign of kidney damage, not creatine use.

Don’t panic if your creatinine is high. Look at the whole picture. If cystatin C and urine protein are normal, and you feel fine, you’re probably okay. But if multiple markers are off - especially protein or BUN - then it’s time to talk to a nephrologist.

What You Should Do Before and While Taking Creatine

If you have kidney disease or are on kidney medications, don’t skip creatine without a plan. Here’s how to do it safely:

1. Get baseline labs - Before starting creatine, ask for a full kidney panel: serum creatinine, cystatin C, BUN, urine protein, and eGFR (both creatinine-based and cystatin C-based). Keep a copy.
2. Start low - Skip the loading phase. Go straight to 3 grams a day. No need to flood your system.
3. Monitor every 3 months - Repeat the same labs. Compare to your baseline. If cystatin C stays flat and your eGFR (CysC) doesn’t drop, you’re good.
4. Tell every doctor - Write it on your medication list. Say it out loud. “I take 3 grams of creatine daily.” Don’t assume they know. Most don’t.
5. Stop if things change - If your cystatin C rises, or your BUN climbs, or you start swelling or feeling tired, pause creatine and get retested.

The National Kidney Foundation says creatine is safe for healthy people. But for those with kidney disease? They say: “Use with caution and proper monitoring.” That’s not a warning. It’s a roadmap.

What Your Doctor Should Be Doing

Most doctors aren’t trained to handle this. But they should be.

• Ask about supplements - every time. Not just prescription drugs. Creatine is the #1 supplement used by adults under 45.
• Order cystatin C when creatinine is high - especially in athletes or gym-goers.
• Know the difference between creatine-induced elevation and real kidney disease - one is harmless, the other is serious.
• Don’t refer someone to a nephrologist just because creatinine is high. Look at cystatin C first.

There’s a growing push to adjust eGFR formulas to account for creatine use. Early research from the University of Toronto suggests multiplying the creatinine-based eGFR by 0.9 for creatine users. That’s not official yet - but it’s coming.

The Bottom Line

Creatine doesn’t break your kidneys. But it can trick your labs into thinking it did. If you’re on kidney disease meds, you’re already walking a tightrope. Don’t let a supplement make the fall worse - or worse, make you think you’re falling when you’re not.

Take creatine if you want to. Just know how to read the numbers. Get cystatin C tested. Talk to your doctor. Keep records. You’re not risking your kidneys - you’re protecting your peace of mind.