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 limits the activity of these enzymes outside cells, which protects tissues.
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 and varies little with diet. Its level rises gradually with age, which the eGFR calculation accounts for. This constancy makes it a more faithful marker of actual kidney function, especially in muscular or elderly individuals.
Reference Ranges
Depending on the biomarker, Singular ranges are based on a synthesis of nutritional or clinical reference points and longevity research. They do not replace your laboratory's reference values or your healthcare professional's advice.
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 sit within the interval expected in adults. The overall reading of filtration comes from the combined eGFR, computed with creatinine. 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 points to a muscular effect on creatinine, without establishing it on its own.
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 does not change its concentration. A randomized trial measured no effect of creatine supplementation on this marker.
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. 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 a signal independent of muscle. Cross-reading both markers distinguishes a muscular variation from an actual change in glomerular filtration.
When the combined eGFR sits in its lowest range, Singular applies a precaution: magnesium, creatine, iodine, glucosamine and taurine are withdrawn from the formula, and vitamin C intake is capped. This precaution follows the combined eGFR, not cystatin C on its own.
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. Development on 5,352 participants for the combined equation, independent validation on 4,050. International reference equations for glomerular filtration rate estimation. | ||||
| 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. A meta-analysis predating the 2010 international standardization of assays, on heterogeneous methods. | ||||
| 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 | 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 | 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. | ||||
| Coll E et al. | 2000 | Observational Study | Am J Kidney Dis | View on PubMed |
Serum cystatin C as a new marker for noninvasive estimation of glomerular filtration rate and as a marker for early renal impairment Comparison of cystatin C and creatinine against a reference clearance: sensitivity of 93.4% versus 86.8%, and a rise detectable from 88 mL/min/1.73 m² versus 75. A single-center study from 2000, with twenty controls with normal kidney function and an assay predating international standardization. | ||||
| Jung E et al. | 2022 | Meta-analysis | Biomarkers | View on PubMed |
Cystatin C and mortality risk in the general population: systematic review and dose response meta-analysis Meta-analysis of thirteen prospective cohorts, that is 57,214 participants: the relationship between cystatin C and cardiovascular mortality is log-linear, each rise of 0.1 mg/L going with a 7.3% higher risk. The ratio between the highest and lowest levels reaches 2.01 for all-cause mortality. | ||||
| Knight EL et al. | 2004 | Observational Study | Kidney Int | View on PubMed |
Factors influencing serum cystatin C levels other than renal function and the impact on renal function measurement Cross-sectional study of 8,058 inhabitants of Groningen: after adjusting for creatinine clearance, older age, male sex, weight, height, smoking and C-reactive protein remain associated with higher cystatin C. The marker therefore depends on factors other than kidney function alone. | ||||