Cystatin C

What Is Cystatin C?

Cystatin C is a low–molecular-weight protein produced by all nucleated cells. As a cysteine protease inhibitor, it regulates enzymes that degrade proteins, helping maintain cellular integrity. Clinically, Cystatin C serves as a sensitive indicator of kidney function: it is freely filtered by glomeruli and not reabsorbed, so rising blood levels reflect a declining glomerular filtration rate (GFR).

Why It Outperforms Creatinine

Unlike serum creatinine, Cystatin C levels remain stable regardless of muscle mass, diet, age, or gender. This makes it particularly valuable in populations where creatinine is unreliable—such as patients with liver cirrhosis, malnutrition, limb amputations, or reduced muscle mass (elderly and pediatric patients). In cases of mild GFR reduction (45–59 mL/min), combining Cystatin C and creatinine enhances diagnostic precision.

Clinical Implications of Cystatin C Levels

Low Cystatin C

Levels below the optimal window indicate a higher GFR and robust renal clearance—generally a positive finding in healthy individuals.

High Cystatin C

Elevated Cystatin C suggests impaired renal filtration and correlates with increased risk of:

• Cardiovascular disease and heart failure
  
• Venous thromboembolism
  
• Neurodegenerative disorders such as Alzheimer’s disease
  
• Inflammation: reflected by concurrent rises in C-Reactive Protein
  
• Thyroid dysfunction, especially hyperactive thyroid
  
• Elevated homocysteine: a marker of vascular risk (homocysteine)
  
• Malignancy, HIV/AIDS, rheumatic diseases, and corticosteroid therapy

High Cystatin C is also an independent predictor of all-cause mortality.

Factors That Influence Cystatin C

• Interfering Conditions: Uncontrolled thyroid disease and kidney transplant status can skew results.
  
• Medications: Corticosteroids elevate Cystatin C; other nephrotoxic drugs may indirectly alter levels.

Clinicians should review medication history and coexisting conditions when interpreting Cystatin C.

Standard and Optimal Ranges

• Standard Range: 0.50–1.00 mg/L
  
• Optimal Range: 0.62–0.90 mg/L

Values within the optimal window generally denote stable renal function. Deviations prompt further evaluation of GFR, cardiovascular health, and systemic inflammation.

In conclusion, a comprehensive evaluation by a functional medicine telehealth provider in Florida integrates Cystatin C into a broader framework of root-cause analysis. By combining evidence-based allopathic therapies with a functional medicine integrative approach—encompassing advanced biomarker profiling, personalized nutrition and lifestyle plans, and targeted therapies—this model addresses underlying pathophysiology rather than merely treating symptoms. Recognizing that true health begins at the cellular level, this strategy lays the groundwork for resilience, preventive care, and longevity. Explore our Regenerative Medicine service to further enhance your wellness journey.

Further Reading

• Reed, C. H. (2000). Diagnostic applications of cystatin C. British Journal of Biomedical Science, 57(4), 323-329. https://pubmed.ncbi.nlm.nih.gov/11204865/

• Inker, L. A., Eneanya, N. D., Coresh, J., Tighiouart, H., Wang, D., Sang, Y., … & Levey, A. S. (2022). Advantages, limitations, and clinical considerations in the adoption of cystatin C in the United States. American Journal of Kidney Diseases, 80(3), 335-344. https://pubmed.ncbi.nlm.nih.gov/36514729/

• Kar, S., Paglialunga, S., & Islam, R. (2018). Cystatin C is a more reliable biomarker for determining eGFR to support drug development studies. Journal of Clinical Pharmacology, 00(0), 1-9. https://www.celerion.com/wp-content/uploads/2018/05/052018_Journal-of-Clinical-Pharmacology_Celerion_Cystatin-C-Is-a-More-Reliable-Biomarker-for-Determining-eGFR-to-Support-Drug-Development_F.pdf

• Sharma, A., & Kaur, J. (2018). Serum cystatin C for evaluation of acute kidney injury in adults on colistin treatment. Indian Journal of Pharmacology, 50(1), 20-25. https://pubmed.ncbi.nlm.nih.gov/30622984/