---
title: "Cystatin C (Renal Filtration Marker) Optimal Range vs Lab Normal (2026 Clinical Decoder & Protocol) | Nutrition Research Labs"
source_url: "https://nutritionresearchlabs.com/biomarkers/cystatin-c"
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description: "Decode your Cystatin C (Renal Filtration Marker) (Cystatin-C) blood test: Longevity Optimal Target (0.55–0.85 mg/L) vs Standard Lab Normal (0.55–1.15 mg/L), assay interference, and Grade-A clinical protocols."
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---

> **Canonical Source:** [https://nutritionresearchlabs.com/biomarkers/cystatin-c](https://nutritionresearchlabs.com/biomarkers/cystatin-c)
>
> *Decode your Cystatin C (Renal Filtration Marker) (Cystatin-C) blood test: Longevity Optimal Target (0.55–0.85 mg/L) vs Standard Lab Normal (0.55–1.15 mg/L), assay interference, and Grade-A clinical protocols.*

## Reference Range Comparison (mg/L)

- **Longevity & Metabolic Optimal Range:** 0.55 – 0.85 mg/L
- **Standard Lab Reference Interval ("Normal"):** 0.55 – 1.15 mg/L
- **Why Standard Lab Ranges Mislead Patients:** Unlike serum creatinine, Cystatin C is completely independent of skeletal muscle mass, dietary meat intake, and creatine supplementation. Muscular athletes are routinely misdiagnosed with kidney disease based on creatinine-eGFR when their Cystatin C-eGFR is perfectly optimal.
- **Pre-Draw Supplement Assay Interference Warning:** Severe untreated thyroid dysfunction alters Cystatin C turnover (hypothyroidism lowers Cystatin C, hyperthyroidism increases it). High-dose glucocorticoid therapy also upregulates Cystatin C production independent of renal filtration.

## Decode the Next Biomarker on Your Blood Panel

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