Cystatin C
The optimal range for Cystatin C (Cystatin C) is commonly cited as 0.5–0.9 mg/L, tighter than the standard lab reference range of 0.5–1.0 mg/L. Kidney function marker independent of muscle mass - more accurate than creatinine in the muscular, elderly, or ill.
How Cystatin C ranges relate
The standard lab range vs the optimization-focused target. Illustrative trajectory shows what a 12-week improvement pattern looks like — not real user data.
What Cystatin C Measures
Cystatin C is a low-molecular-weight protein produced by all nucleated cells at a steady rate, freely filtered by the glomerulus, and not secreted. Unlike creatinine (which varies with muscle mass), cystatin C gives a cleaner read on glomerular filtration rate - particularly in populations where creatinine misleads (very muscular individuals, the elderly, patients with sarcopenia).
Cystatin-based eGFR equations (like CKD-EPI cystatin) are increasingly used in research and complex clinical cases.
What Affects This Biomarker
Cystatin C is influenced by: glomerular filtration rate (the signal of interest), thyroid disease (hyperthyroidism raises), corticosteroid use (raises), and some inflammatory states. Unaffected by muscle mass, diet, or recent exercise - its main advantages.
In the Context of Peptide Protocols
Optional add-on when creatinine-based eGFR is ambiguous (e.g., very muscular lifters often show artificially low eGFR on creatinine). If available, run alongside creatinine every 6–12 months in peptide users.
Frequently Asked Questions
What does Cystatin C measure?
Cystatin C is a low-molecular-weight protein produced by all nucleated cells at a steady rate, freely filtered by the glomerulus, and not secreted. Unlike creatinine (which varies with muscle mass), cystatin C gives a cleaner read on glomerular filtration rate - particularly in populations where creatinine misleads (very muscular individuals, the elderly, patients with sarcopenia).
What is the optimal range for Cystatin C?
The optimal range for Cystatin C is commonly cited as 0.5–0.9 mg/L. The standard lab reference range is 0.5–1.0 mg/L.
What affects Cystatin C levels?
Cystatin C is influenced by: glomerular filtration rate (the signal of interest), thyroid disease (hyperthyroidism raises), corticosteroid use (raises), and some inflammatory states. Unaffected by muscle mass, diet, or recent exercise - its main advantages.
Where This Fits in Your Panel
Cystatin C is one marker on a fuller panel. The Peptide Blood Work Checklist lays out the complete baseline panel, what to add by protocol type, and when to retest.
See the full blood work checklist →Upload any lab PDF and MyProtocolStack maps your values to Cystatin C and 40+ other biomarkers. StackAI interprets the trend in context of your protocol.
Start tracking →Last reviewed: June 2026
Informational only - not medical advice. Reference ranges vary by lab and individual context. Work with a licensed provider to interpret your specific results.