Cystatin C and Kidney Health: A Smarter Way to Check Your Kidneys

Think creatinine is the only way to test your kidneys? It’s time to meet Cystatin C—a smarter, more reliable marker of kidney function.

If you’re concerned about your kidney health or have been monitoring kidney function through traditional blood tests, you’ve likely heard of creatinine and eGFR. While these are helpful, a growing number of experts and researchers including the National Kidney Foundation now recognize that Cystatin C may provide a clearer, more accurate picture.

In this article, we’ll break down what Cystatin C is, why it matters, and how it fits into a more advanced approach to evaluating kidney disease.

What Is Cystatin C and Why Is It Important for Kidney Function?

Cystatin C is a protein made by nearly all cells in your body and released into the bloodstream at a constant rate. Because of its small size, it’s easily filtered by the kidneys.

What makes it unique? Unlike creatinine, which is influenced by muscle mass, age, gender, and diet, Cystatin C levels are far less affected by these external factors. This makes it a more sensitive and reliable marker of kidney function, especially in people with extremes of body composition or those with early kidney changes.

How Does Cystatin C Compare to Creatinine?

Creatinine is a waste product from muscle metabolism. While commonly used to estimate GFR (glomerular filtration rate), it doesn’t always tell the full story. That’s because creatinine levels vary based on how much muscle you have, your hydration status, and your overall diet.

In contrast, Cystatin C offers a more consistent baseline. For patients with unusually high or low muscle mass, such as athletes, elderly individuals, or people with chronic illnesses, Cystatin C may offer a better way to assess kidney function than creatinine.

What Is the Cystatin C Test and How Is It Done?

The Cystatin C test is a simple blood test that measures the concentration of Cystatin C in your blood. It’s quick, non-invasive, and does not require any special preparation like fasting.

Healthcare providers may order this test alone or in combination with creatinine to estimate GFR using newer equations, such as the CKD-EPI Creatinine–Cystatin C formula. This dual approach often provides a more accurate estimated glomerular filtration rate (eGFR).

Who Should Consider Getting a Cystatin C Test?

A Cystatin C test may be used when:

• There’s uncertainty about the accuracy of your creatinine-based eGFR
• You have unusual muscle mass (very low or very high)
• You’re over age 65 and your creatinine level appears “normal”
• You’ve had a kidney transplant or are at risk of chronic kidney disease (CKD)

The National Kidney Foundation supports using Cystatin C in select patients to improve early detection of kidney disease.

Can Cystatin C Improve Accuracy of eGFR?

Yes.

Cystatin C-based equations have become part of the latest CKD guidelines to help refine how we measure kidney function.

By combining serum creatinine and cystatin c, we reduce the margin of error in GFR estimation. That’s especially useful for people with borderline creatinine levels or conflicting test results.

These formulas are particularly valuable in patients at risk of acute kidney injury, early-stage CKD, or certain types of kidney disease that don’t show obvious signs on standard labs.

What Do the Test Results Mean?

Here’s a simple guide to interpreting Cystatin C levels:

• A high level of Cystatin C may suggest your kidneys are not working well.
• A low or normal level typically means your kidneys are filtering properly.

Because this is still a relatively new test, your provider may use it alongside creatinine, UACR (urine albumin-to-creatinine ratio), and possibly imaging or even a kidney biopsy to fully assess kidney health.

How Does Cystatin C Help Monitor Kidney Function Over Time?

For people with known kidney disease or those on medications that affect the kidneys, monitoring kidney function with Cystatin C can provide more consistent tracking over time.

It’s especially valuable when creatinine levels fluctuate due to changes in muscle mass, hydration, or illness. When used regularly, Cystatin C can help detect early changes in renal function, allowing for timely intervention and prevention of further kidney damage.

Are There Any Limitations to the Cystatin C Test?

Yes.

While promising, Cystatin C testing isn’t perfect. Limitations include:

• Higher cost compared to creatinine testing
• Not yet available in all labs or hospitals
• Less data in certain populations (e.g. children or severely ill patients)
• Influences from inflammation or steroid use that can skew results

Still, for many patients, the value of Cystatin C lies in offering a clearer, more personalized measure of kidney function than creatinine alone.

How Does Cystatin C Fit Into a Complete Kidney Health Check?

A full kidney function assessment may include:

• Serum creatinine and creatinine clearance
• Cystatin C test
• eGFR (estimated glomerular filtration rate)
• Urine test for albumin or protein
• Imaging tests (e.g. ultrasound)
• Possibly a kidney biopsy if deeper evaluation is needed

Combining these tests to check kidney health gives a more comprehensive view—especially in patients with unexplained symptoms, chronic illnesses, or those receiving kidney transplant follow-up.

Why Early Detection Using Cystatin C Matters

The earlier you catch kidney disease, the better your chances of protecting your long-term health. Delayed diagnosis can lead to irreversible kidney damage, dialysis, or even kidney failure.

By using Cystatin C early (especially in high-risk patients) you gain the advantage of more precise monitoring and the ability to adjust treatment before complications arise.

Summary: What to Know About Cystatin C

• Cystatin C is a protein filtered by the kidneys and a reliable marker of kidney function
• It’s less affected by muscle mass than creatinine
• Helps provide a more accurate eGFR when used alone or with creatinine
• Ideal for people with unusual body composition or borderline creatinine levels
• Supported by the National Kidney Foundation and Kidney Disease Improving Global Outcomes (KDIGO) guidelines
• Plays a key role in the early detection of kidney disease

Further Reference

1. Cystatin C [Internet]. National Kidney Foundation. 2024. Available from: https://www.kidney.org/kidney-topics/cystatin-c
2. Fernando S, Polkinghorne KR. Cystatin C: not just a marker of kidney function. Brazilian Journal of Nephrology [Internet]. 2020 Apr 3;42(1):6–7. 
3. Chen DC, Potok OA, Rifkin D, Estrella MM. Advantages, Limitations, and Clinical Considerations in Using Cystatin C to Estimate GFR. Kidney360 [Internet]. 2022 Aug 23;3(10):1807–14. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9717651/
4. Shlipak MG, Matsushita K, Ärnlöv J, Inker LA, Katz R, Polkinghorne KR, et al. Cystatin C versus Creatinine in Determining Risk Based on Kidney Function. New England Journal of Medicine. 2013 Sep 5;369(10):932–43.
5. Lees JS, Rutherford E, Stevens KI, Chen DC, Scherzer R, Estrella MM, et al. Assessment of Cystatin C Level for Risk Stratification in Adults With Chronic Kidney Disease. JAMA Network Open. 2022 Oct 25;5(10):e2238300.