Cystatin C Normal Ranges in Adults
The normal reference range for serum cystatin C in adults is approximately 0.50-1.02 mg/L, with values varying slightly by age and sex. 1
Age-Specific Reference Values
Adults aged 20-59 years:
Adults ≥60 years: 0.83 ± 0.103 mg/L for both sexes, reflecting physiological aging of renal function 2
Children aged 4-19 years: 0.75 ± 0.089 mg/L 2
Key Clinical Considerations
The most commonly cited reference interval across multiple studies is 0.51-1.02 mg/L (median 0.79 mg/L) for general adult populations. 1 However, important variations exist:
A large French study of 1,223 subjects demonstrated Gaussian distribution with slightly lower values in females compared to males under age 60 2
Saudi population data showed a mean of 0.751 ± 0.11 mg/L with a 95% reference range of 0.53-0.95 mg/L 3
Japanese studies reported reference intervals of 0.47-1.03 mg/L 4
Factors Affecting Cystatin C Levels
Unlike creatinine, cystatin C is largely independent of muscle mass, making it superior for patients with variable muscle mass, malnutrition, or extremes of body composition. 5
Age: Levels increase significantly after age 60 due to physiological decline in GFR 2
Sex: Females have slightly lower values than males in the 20-59 age range, but this difference disappears after age 60 2
Body mass index: Shows only moderate correlation without biological significance 2
Medications: Methylprednisolone increases levels; cyclosporin A decreases levels 2
Clinical Interpretation
Cystatin C begins to rise above normal when GFR falls below 94.4 mL/min (135.9 L/day), making it more sensitive than creatinine for detecting early renal impairment. 4 This represents a critical advantage, as serum creatinine may remain within normal ranges at this level of GFR reduction.
The 2012 CKD-EPI cystatin C equation uses 0.8 mg/L as the reference point in its formula for estimating GFR 6
KDIGO 2024 guidelines recommend cystatin C-based equations specifically for patients with stage 3a CKD (eGFR 45-59 mL/min/1.73m²) and variable muscle mass to confirm CKD diagnosis 5
Biological Variation
Cystatin C demonstrates superior biological characteristics for detecting impaired renal function compared to creatinine. 7 The critical difference for sequential measurements is 37% for cystatin C versus 14% for creatinine, with intraindividual variance accounting for 75% of cystatin C biological variation versus only 7% for creatinine 7. This means the upper limit of the reference interval for cystatin C is typically only 3-4 standard deviations from any individual's mean value, whereas for creatinine this can range from 2-13 standard deviations depending on the individual 7.