Physiological Role
Cystatin C is a small 13 kDa protein produced at a constant rate by all nucleated cells in the body. It belongs to the cysteine protease inhibitor family and plays a role in regulating intracellular protein degradation.
Its distinctive feature lies in its elimination pathway. Cystatin C is freely filtered by the glomeruli (the kidneys’ filtration units), then reabsorbed and degraded by the proximal tubules. It does not return to the bloodstream after filtration. Its plasma concentration therefore directly reflects the glomerular filtration rate (GFR), the speed at which the kidneys filter blood.
Unlike creatinine, cystatin C does not depend on muscle mass. It is produced steadily, regardless of sex, age, or diet. This constancy makes it a more faithful marker of actual kidney function, especially in muscular or elderly individuals.
Reference Ranges
These reference ranges are derived from scientific literature and may differ from your laboratory's reference values.
Biological Significance
Cystatin C is now recognised as a more sensitive marker of glomerular filtration than creatinine in many clinical contexts. It rises when GFR drops below 88 mL/min/1.73 m2, versus 75 for creatinine. This sensitivity provides an earlier observation window.
Values in the optimal range indicate functional and efficient kidney filtration. Elevated values may reflect a slowdown in glomerular filtration. The value of cystatin C also lies in cases of discordance with creatinine. In muscular individuals, elevated creatinine with normal cystatin C confirms a muscular origin, not renal.
The combined CKD-EPI 2021 equation, published in the New England Journal of Medicine, integrates both markers for GFR estimation without a race variable. This approach compensates for the respective limitations of each marker and improves longitudinal monitoring precision.
Cystatin C is also studied as a predictive marker of cardiovascular risk and all-cause mortality, beyond its renal role. Large cohorts have linked elevated levels to higher cardiovascular event risk, independent of estimated GFR.
Influencing Factors
Age. Cystatin C increases progressively with age, reflecting the physiological decline of glomerular filtration. This gradual rise makes it a relevant marker of kidney ageing.
Inflammation. Chronic inflammatory status can elevate cystatin C independently of kidney function. C-reactive protein (hs-CRP), measured by Singular, helps contextualise this elevation.
Thyroid function. Hyperthyroidism tends to increase cystatin C, while hypothyroidism decreases it. TSH, also tracked by Singular, helps interpret these variations.
Corticosteroid therapy. High-dose corticosteroids can increase cystatin C production by nucleated cells, independently of any change in kidney filtration.
Body composition. Unlike creatinine, cystatin C is not influenced by muscle mass. However, severe obesity is associated with slightly higher levels, possibly linked to low-grade inflammation from adipose tissue.
Smoking. Tobacco use is associated with a moderate elevation of cystatin C, likely through its effects on systemic inflammation and endothelial function.
Hydration and diet. Cystatin C is largely insensitive to short-term dietary variations, unlike creatinine. A high-protein diet or creatine supplementation does not affect its production rate.
In the Singular Formula
Cystatin C is a monitoring parameter integrated into the Singular biological profile. It is not associated with any direct adjustment rule in the formulation engine. Its role is to provide a reliable reading of kidney function, free from the muscular biases of creatinine.
The kidneys eliminate metabolites from many bioactives in the formula. A stable GFR, confirmed by cystatin C, indicates that renal elimination function supports tolerance to calibrated dosages. Singular uses the combined GFR (CKD-EPI 2021 equation, creatinine + cystatin C) as the derived marker for this assessment.
Cystatin C complements creatinine in the Singular kidney panel. Where creatinine can be skewed by muscle mass or creatine supplementation, cystatin C provides an unambiguous signal. Cross-reading both markers distinguishes a muscular variation from an actual change in glomerular filtration.
Scientific Studies
| Authors | Year | Type | Journal | |
|---|---|---|---|---|
| Inker LA et al. | 2021 | Cohort Study | N Engl J Med | View on PubMed |
New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race New CKD-EPI 2021 equations incorporating cystatin C, alone or combined with creatinine, to estimate GFR without a race variable. Validated on over 8,000 participants, now the current standard. | ||||
| Shlipak MG et al. | 2013 | Meta-analysis | N Engl J Med | View on PubMed |
Cystatin C versus Creatinine in Determining Risk Based on Kidney Function Meta-analysis of 11 cohorts (90,750 participants) showing that cystatin C, alone or combined with creatinine, strengthens the association between estimated GFR and risks of death and end-stage kidney failure. | ||||
| Dharnidharka VR et al. | 2002 | Meta-analysis | Am J Kidney Dis | View on PubMed |
Serum Cystatin C Is Superior to Serum Creatinine as a Marker of Kidney Function: A Meta-Analysis Meta-analysis of 46 studies showing a higher correlation between cystatin C and GFR compared to serum creatinine, confirming its superiority as a kidney function marker. | ||||
| Shlipak MG et al. | 2005 | Cohort Study | N Engl J Med | View on PubMed |
Cystatin C and the Risk of Death and Cardiovascular Events among Elderly Persons Cohort study demonstrating a dose-response association between elevated cystatin C levels and increased risk of all-cause mortality and cardiovascular events in elderly persons. | ||||
| Onopiuk A et al. | 2015 | Systematic Review | Adv Clin Chem | View on PubMed |
Cystatin C: A Kidney Function Biomarker Comprehensive review of the biological role of cystatin C, its measurement methods, and its clinical applications as a kidney function biomarker. | ||||
| Shlipak MG et al. | 2013 | Systematic Review | Am J Kidney Dis | View on PubMed |
Update on Cystatin C: Incorporation into Clinical Practice Literature synthesis on integrating cystatin C into KDIGO guidelines and practical approaches for clinicians seeking to incorporate this marker into practice. | ||||
| Koenig W et al. | 2005 | Cohort Study | Clin Chem | View on PubMed |
Plasma Concentrations of Cystatin C in Patients with Coronary Heart Disease and Risk for Secondary Cardiovascular Events: More Than Simply a Marker of Glomerular Filtration Rate Study showing that elevated cystatin C concentrations in individuals with coronary heart conditions are associated with increased risk of secondary cardiovascular events, beyond glomerular filtration rate. | ||||