Cystatin C
Sensitive kidney filter marker independent of muscle mass – superior GFR estimator
Also known as
Definition
Cystatin C is a low-molecular-weight protein (cysteine protease inhibitor) produced constantly by all nucleated body cells and eliminated exclusively through glomerular filtration. Unlike creatinine, cystatin C is independent of muscle mass, sex, and diet — making it a superior endogenous GFR marker, particularly in borderline cases and individuals with extreme body compositions (muscular athletes, cachectic patients, the elderly).
| Parameter | Value |
|---|---|
| Unit | mg/l |
| Reference Range | 0.50–1.00 mg/l (adults; mild rise with age, diabetes, and inflammation) |
| Optimal Range (lab2go) | < 0.85 mg/l (lab2go Optimum Zone — values < 0.85 mg/l associated with GFR equivalent > 90 ml/min/1.73 m²; more strongly linked to mortality than creatinine) |
↓ What a low value means
Very low cystatin C values (< 0.5 mg/l) are rare and clinically insignificant. Theoretically, hyperthyroidism-induced higher cell proliferation rates may mildly increase (not decrease) production. No relevant pathology known at low values.
↑ What a high value means
Elevated cystatin C (> 1.0 mg/l) indicates impaired glomerular filtration (chronic kidney disease, CKD). Advantage over creatinine: detects mild GFR impairment (GFR 60–90 ml/min) in patients with low creatinine due to reduced muscle mass (elderly women, cachectic patients). Elevated cystatin C is also an independent cardiovascular risk marker.
✓ How to optimize this marker
Cystatin C reflects kidney filtration; optimize by: blood pressure control (< 130/80 mmHg protects the kidney), adequate hydration, reducing nephrotoxic substances (NSAIDs, contrast agents), optimizing diabetes control, protein-adjusted diet in CKD (0.8 g/kg/day). ACE inhibitors/ARBs protect kidneys in diabetes with proteinuria.
When to test
When creatinine-based GFR appears suspicious with normal creatinine (low muscle mass), in older patients, for mild CKD evaluation (G2 stage), cardiovascular risk assessment, and medication dose adjustment. CKD-EPI with cystatin C alone or combined with creatinine is the most precise GFR estimator.
Frequently asked questions
Why is cystatin C better than creatinine for older adults? +
Creatinine is released from muscles — older adults lose muscle mass (sarcopenia) and produce less creatinine even as kidney function declines. Normal creatinine can mask a GFR of only 45 ml/min in a low-muscle 80-year-old. Cystatin C is produced independently of muscle mass and reliably detects this hidden kidney impairment.
Does inflammation affect cystatin C measurement? +
Yes. Pro-inflammatory cytokines (IFN-γ, IL-2) can raise cystatin C production by 10–20%, independent of kidney function. Thyroid function also influences cystatin C (hyperthyroidism raises, hypothyroidism mildly lowers it). These factors should be considered when interpreting results — GFR from cystatin C may be mildly underestimated during active inflammation.
Do I need to fast for a cystatin C measurement? +
No. Unlike creatinine, cystatin C varies little with meals or time of day. It can be measured at any time. Only after very protein-rich meals (> 80 g protein) do studies show minor rises, which are not clinically relevant.
When is cystatin C preferred over creatinine? +
Cystatin C is preferred for: older patients (> 65 years), extreme muscle mass (bodybuilders with high-normal creatinine), cachectic patients, cancer patients, bariatric surgery (rapid weight loss), and when precise GFR estimation for drug dosing is important. The CKD-EPI 2021 cystatin C formula is currently the gold standard.
Sources
- Shlipak MG et al. (2013) Cystatin C versus Creatinine in Determining Risk Based on Kidney Function. N Engl J Med.
- KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int Suppl.
- Inker LA et al. (2021) New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race. N Engl J Med.
Last Reviewed: May 28, 2026 · sina
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.