Cystatin C

Kidney Function marker

Cystatin C

Category: Kidney Function
Unit: mg/L

Small protein filtered by the kidneys. Unlike creatinine, Cystatin C is not affected by muscle mass, making it a more accurate kidney function marker for muscular individuals.

PED Notes

CRITICAL: The gold-standard kidney marker for athletes with high muscle mass. Creatinine-based eGFR is unreliable in muscular individuals because creatinine scales with muscle mass, giving falsely 'elevated' readings and falsely low eGFR. Cystatin C-based eGFR removes this confounder entirely. If creatinine is elevated but Cystatin C is normal, kidney function is fine — the creatinine elevation is from muscle mass. Request this test whenever creatinine or eGFR results are ambiguous. Especially important when using nephrotoxic compounds (Trenbolone, high-dose orals) or chronic NSAID use.

Why Cystatin C Matters for Athletes:

  • Unlike creatinine, Cystatin C is NOT affected by muscle mass, diet, or exercise
  • Provides accurate kidney function assessment when creatinine is unreliable
  • Request Cystatin C-based eGFR calculation from your lab for the most accurate GFR

If Elevated (>1.15 mg/L):

  • Indicates genuine kidney function impairment (unlike creatinine, this is NOT a false positive from muscle)
  • Evaluate current compound use — trenbolone and high-dose oral AAS are most nephrotoxic
  • Assess NSAID use (ibuprofen, naproxen) — chronic use damages kidneys
  • Check blood pressure (hypertension damages kidneys over time)

Supplements:

  • Astragalus -- 500-1000mg/day (renoprotective properties)
  • Omega-3 Fish Oil -- 2-4g/day (anti-inflammatory, renal protective)
  • CoQ10 -- 100-200mg/day (antioxidant support for renal cells)

Lifestyle:

  • Hydrate well (3-4L/day)
  • Limit NSAID use — use paracetamol or topical alternatives for pain
  • Monitor blood pressure (target <130/80)
  • If persistently elevated, nephrology referral recommended

References:

  • Zhang, H. W., Lin, Z. X., Xu, C., Leung, C., & Chan, L. S. (2014). Astragalus (a traditional Chinese medicine) for treating chronic kidney disease. Cochrane Database of Systematic Reviews, 2014(10), CD008369. DOI: 10.1002/14651858.CD008369.pub2
  • Calder, P. C. (2017). Omega-3 fatty acids and inflammatory processes: From molecules to man. Biochemical Society Transactions, 45(5), 1105-1115. DOI: 10.1042/BST20160474
  • Garrido-Maraver, J., Cordero, M. D., Oropesa-Avila, M., et al. (2014). Coenzyme Q10 therapy. Molecular Syndromology, 5(3-4), 187-197. DOI: 10.1159/000360101

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Frequently Asked Questions

Reference Ranges

Standard Range

0.55 - 1.15 mg/L

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