Cystatin C
Also known as: Cys C
What Does Cystatin C Measure?
Cystatin C is a small protein produced by virtually all nucleated cells in the body at a constant rate. Unlike other kidney markers, its production is not significantly affected by age, sex, muscle mass, or diet, making it a particularly reliable indicator of kidney filtration function. Blood tests measure the concentration of cystatin C in the serum, which reflects how efficiently the kidneys are filtering waste from the blood — a function known as the glomerular filtration rate (GFR).
Why Does Cystatin C Matter?
Cystatin C is considered a more sensitive and earlier indicator of kidney dysfunction than the traditional marker creatinine, especially in populations where creatinine can be misleading — such as elderly individuals, people with low muscle mass, or those who are malnourished. Elevated cystatin C levels can detect mild declines in kidney function (chronic kidney disease stages 1-2) before creatinine levels rise noticeably. Beyond kidney health, elevated cystatin C is also associated with increased cardiovascular risk, heart failure, and mortality, making it a valuable marker for overall health assessment.
Normal Ranges
Males
0.62–1.15 mg/L
Females
0.62–1.15 mg/L
Children
Varies by age; newborns: 1.49–2.85 mg/L, decreasing to adult levels by approximately 1–2 years of age
Causes of High Levels
- Chronic kidney disease (CKD) — reduced glomerular filtration rate causes cystatin C to accumulate in the blood
- Acute kidney injury — sudden loss of kidney function leads to rapid rise in cystatin C levels
- Diabetes mellitus — diabetic nephropathy damages kidney filtering units over time
- Hypertension — sustained high blood pressure can damage kidney blood vessels and impair filtration
- Hyperthyroidism — thyroid hormones stimulate increased production of cystatin C independent of kidney function
- Corticosteroid use — glucocorticoid medications can raise cystatin C levels without necessarily reflecting true kidney impairment
Causes of Low Levels
- Hypothyroidism — reduced thyroid hormone levels lower the production rate of cystatin C
- Immunosuppressive therapy — certain medications such as cyclosporine may reduce cystatin C production in some contexts
How to Improve Your Cystatin C
Diet
- Reduce sodium intake to less than 2,300 mg per day to lower blood pressure and reduce kidney strain
- Limit dietary protein to 0.6–0.8 g/kg body weight per day in those with established kidney disease to reduce filtration burden
- Increase consumption of fruits and vegetables (plant-based diet) to reduce dietary acid load and support kidney health
- Minimize processed foods, red meat, and high-phosphorus foods to reduce metabolic waste the kidneys must filter
- Stay well-hydrated with 6–8 glasses of water daily to support kidney perfusion and filtration
Supplements
- Omega-3 fatty acids (2–4 g/day of EPA+DHA) — shown to reduce inflammation and may support kidney function
- Coenzyme Q10 (100–300 mg/day) — antioxidant support that may protect kidney cells from oxidative damage
- Vitamin D3 (1,000–2,000 IU/day, with physician guidance) — deficiency is common in CKD and may worsen kidney and cardiovascular outcomes
- Magnesium glycinate (200–400 mg/day) — supports blood pressure regulation and may reduce kidney stress
- Probiotic supplementation — emerging evidence suggests gut microbiome modulation may reduce uremic toxins and support kidney health
Related Biomarkers
Frequently Asked Questions
Is cystatin C better than creatinine for measuring kidney function?
Cystatin C is generally considered more accurate than creatinine, particularly in older adults, women, people with low muscle mass, and those who are obese or malnourished. Creatinine is derived from muscle metabolism, so people with less muscle produce less creatinine — which can make kidney function appear normal even when it is impaired. Cystatin C is produced at a constant rate by all cells regardless of muscle mass, making it a more reliable and consistent marker. Many clinical guidelines now recommend using both markers together (CKD-EPI cystatin C equation) for the most accurate GFR estimation.
What level of cystatin C indicates kidney disease?
A cystatin C level above 1.15 mg/L is generally considered above the normal reference range and may indicate reduced kidney filtration. Levels above 1.3–1.5 mg/L are increasingly associated with moderate kidney impairment. However, values must be interpreted alongside other kidney markers such as creatinine, eGFR, and urine albumin. A single elevated reading does not diagnose chronic kidney disease — persistence over three months or longer is typically required for a CKD diagnosis.
Can cystatin C be elevated without kidney disease?
Yes. Cystatin C can be elevated in conditions unrelated to kidney disease. Hyperthyroidism increases its production rate at the cellular level. High-dose corticosteroid (steroid) therapy is a well-known non-renal cause of elevated cystatin C. Significant inflammation, certain cancers, and HIV infection have also been associated with higher levels. This is why cystatin C results should always be interpreted in clinical context alongside other tests and a physician's assessment.