The Optispan Podcast with Matt Kaeberlein

Is Creatine Harming Your Kidneys? The Blood Test Myth Explained.

9 snips
Sep 16, 2025
Many people experience alarming results on standard kidney tests when taking creatine, raising fears of kidney failure. The discussion clarifies that creatinine and EGFR tests can produce false positives. An alternative marker, Cystatin C, is introduced as a more reliable measure for kidney health. The hosts explain who else might be at risk for these misleading results and emphasize the importance of consulting healthcare professionals for accurate assessments. This conversation debunks myths and empowers listeners to understand their kidney function better.
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INSIGHT

Creatinine Underpins Standard Kidney Tests

  • Creatinine in blood is the standard marker used to estimate kidney function via eGFR.
  • Creatine supplements can raise creatinine because creatine converts into creatinine, skewing eGFR downward.
ANECDOTE

Personal False Positive From Creatine

  • Matt resumed 10 g/day creatine and his creatinine rose to 1.43, triggering an eGFR of 58 flagged as impaired.
  • That single creatinine-based result would have suggested early-stage kidney disease if taken alone.
INSIGHT

Cystatin C Is A More Reliable Marker

  • Cystatin C is produced constantly by all nucleated cells and cleared by the kidneys, making it a stable filtration marker.
  • eGFR can be calculated from cystatin C and avoids the creatine-to-creatinine confounder.
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