Estimated GFR from Cystatin C

Kidney Function marker

eGFR (Cystatin C)

Estimated GFR from Cystatin C

Category: Kidney Function
Unit: mL/min/1.73m2

Estimated glomerular filtration rate calculated from cystatin C using the CKD-EPI 2012 equation. Unlike creatinine-based eGFR, this calculation is not confounded by skeletal muscle mass, dietary protein, or creatine supplementation, making it the gold-standard kidney filtration marker for muscular athletes.

PED Notes

The most accurate eGFR for AAS users, bodybuilders, and creatine supplementers. Creatinine-based eGFR systematically underestimates true GFR in muscular individuals because muscle mass elevates serum creatinine independent of kidney function. Cystatin C-derived eGFR removes that confounder. Inoue et al. (PMID 30630856) and others have shown the cystatin C-based estimate is closer to measured GFR (mGFR by iohexol or inulin clearance) than the creatinine-based estimate in athletes. When creatinine-eGFR is borderline (50-70 mL/min/1.73m2) but cystatin C-eGFR is normal (>=90), kidney function is genuinely fine. When both are reduced, kidney function is genuinely impaired. The 2021 CKD-EPI combined creatinine plus cystatin C equation (eGFRcr-cys) is the most accurate of all, and clinical guidelines now recommend it for staging CKD when the creatinine-only estimate is ambiguous.

When low

Understanding cystatin C-based eGFR:

  • More accurate than creatinine-based eGFR in muscular individuals
  • Not affected by muscle mass, diet, or creatine supplementation
  • The CKD-EPI 2021 combined (creatinine plus cystatin C) equation is the most accurate; the cystatin C-only equation is second-most accurate
  • A normal cystatin C eGFR with a low creatinine eGFR means kidney function is fine and the creatinine elevation is from muscle mass

If genuinely low (<60 mL/min/1.73m2):

  • This reflects real kidney impairment, not a muscle-mass artefact
  • Evaluate current PED stack: trenbolone, high-dose orals (anavar, anadrol, dianabol), and EQ at supratherapeutic doses are the most nephrotoxic
  • Assess NSAID use (ibuprofen, naproxen): chronic use damages glomerular filtration
  • Check blood pressure: untreated hypertension drives CKD progression
  • Repeat in 4-8 weeks to confirm trend before acting

Supplements:

  • Astragalus -- 500-1000mg/day (renoprotective, Cochrane evidence)
  • Omega-3 Fish Oil -- 2-4g/day EPA plus DHA (anti-inflammatory, glomerular protective)
  • CoQ10 -- 100-200mg/day (antioxidant support for renal tubular cells)

Pharmacological options (confirmed eGFR decline below 60):

  • Telmisartan -- 40-80mg/day ARB; first-line renoprotective with PPAR-gamma bonus for AAS users
  • Empagliflozin or Dapagliflozin -- 10-25mg/day SGLT2 inhibitor; EMPA-KIDNEY and DAPA-CKD demonstrated renoprotection independent of diabetes
  • Lisinopril or Ramipril -- alternative ACE inhibitors if ARBs not tolerated; do not combine ACE with ARB (additive hyperkalaemia and AKI risk)
  • All require physician oversight; baseline potassium and eGFR before starting

Lifestyle:

  • Hydrate well (3-4L/day)
  • Limit NSAID use; use paracetamol or topical alternatives
  • Target blood pressure <130/80
  • Reduce AAS dose or discontinue nephrotoxic compounds if eGFR is genuinely declining
  • Nephrology referral if cystatin C eGFR <45 mL/min/1.73m2 or rapidly declining

History Chart

Reading History

Frequently Asked Questions

Reference Ranges

Standard Range

≥ 90 mL/min/1.73m2

VitalMetrics Range

≥ 60 mL/min/1.73m2

Statistics