Why is accurate assessment of kidney function important?
Evaluation of kidney function is a key element in diagnosing and monitoring patients with acute or chronic kidney diseases.
Traditionally, serum creatinine levels are used for this purpose; however, in recent years, another biomarker — Cystatin C — has gained popularity for its higher sensitivity to early kidney function impairment.
What is Cystatin C?
Cystatin C is a protein constantly produced by all nucleated cells of the body and excreted through the kidneys.
It is a sensitive marker of kidney function since its level in the blood increases when the glomerular filtration rate (GFR) decreases [1].
Comparison with creatinine
Creatinine is produced as a result of metabolic processes in muscle tissue, so its blood level largely depends on sex, age, physical activity, and muscle mass.
This means that in individuals with reduced muscle mass (for example, in elderly patients or in cases of sarcopenia and muscular dystrophies), creatinine levels may remain within the normal range even when kidney function is significantly impaired [2].
Meanwhile, the serum level of cystatin C does not depend on muscle mass, sex, or diet, which allows it to respond more rapidly to changes in glomerular filtration [1, 2].
How does Cystatin C work in kidney diagnostics?
Cystatin C is freely filtered in the glomeruli and completely metabolized in the proximal tubules of the nephron.
It does not return to the bloodstream and is not excreted in the urine, making its blood concentration an accurate reflection of the glomerular filtration rate (GFR).
Creatinine is also filtered in the glomeruli, but it is partially secreted in the tubules, which may distort results, especially in the early stages of kidney dysfunction [3].
Advantages of using Cystatin C in clinical practice
Early diagnosis of acute kidney injury
One of the key advantages of Cystatin C is its ability to respond to decreased GFR earlier than creatinine.
In cases of acute kidney injury, blood levels of Cystatin C begin to rise within 12–24 hours after damage, whereas creatinine may remain normal for up to 48 hours [4].
This is critically important for clinical decision-making — early detection of acute kidney injury allows timely therapy adjustment and prevents disease progression.
Detection of chronic kidney disease at an early stage
Cystatin C is better suited for GFR assessment, as in patients with mild kidney function decline, creatinine levels may still remain within reference values.
In contrast, Cystatin C already shows elevation, allowing detection of chronic kidney disease at an early stage.
This is particularly important when screening patients with risk factors such as diabetes, hypertension, and cardiovascular diseases [1].
When is Cystatin C measurement appropriate?
Measuring Cystatin C is appropriate when kidney function assessment by creatinine may be insufficiently accurate or when precision has clinical significance.
That is, for patients:
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with uncertain GFR results (borderline between reference and pathological, without obvious kidney damage);
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with atypical muscle mass;
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for whom accurate kidney function assessment has important clinical relevance (before kidney donation, before surgery, when prescribing nephrotoxic drugs, or during transplantation preparation);
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with chronic kidney disease or at risk of developing it;
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with acute kidney impairment or in conditions where GFR may change rapidly.
Where is it appropriate to implement Cystatin C testing?
This test is suitable for laboratories:
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serving nephrology and cardiology departments;
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within centers for diagnosis of chronic and acute kidney diseases;
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in oncology clinics (for monitoring drug-induced nephrotoxicity);
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in medical centers performing screening and early detection of kidney pathology;
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of a general profile, offering a wide range of studies.
Respons biochemical analyzers — a simple solution for implementation
The series of Respons biochemical analyzers from the trusted manufacturer DiaSys makes it easy to include this test in the range of diagnostic services.
The Respons model line is designed to meet the needs of laboratories with varying workloads — from small facilities to large multidisciplinary medical institutions.
Conclusion: Cystatin C — a marker that changes the approach to kidney diagnostics
The use of Cystatin C enables faster diagnosis of both acute and chronic kidney injuries, which is critical for timely intervention and complication prevention.
In laboratory practice, Cystatin C testing can enhance the diagnostic value of kidney function studies, especially in complex or uncertain cases.
References:
- Chen D.C., Potok O.A., Rifkin D. et al. Advantages, Limitations, and Clinical Considerations in Using Cystatin C to Estimate GFR. KIDNEY360 2022; 3: 1807–1814. doi: https://doi.org/10.34067/KID.0003202022
- Gharaibeh K.A., Hamadah A.M., El-Zoghby Z.M. et al. Cystatin C Predicts Renal Recovery Earlier Than Creatinine Among Patients With Acute Kidney Injury. Kidney Int Rep 2017; 3(2):337-342. doi: 10.1016/j.ekir.2017.10.012
- Li C., Ma Y., Yang C. et al. Association of Cystatin C Kidney Function Measures With Long-term Deficit-Accumulation Frailty Trajectories and Physical Function Decline. JAMA Netw Open. 2022; 5(9):e2234208. doi: 10.1001/jamanetworkopen.2022.34208
- Herget-Rosenthal S., Feldkamp T., Volbracht L. et al. Measurement of urinary cystatin C by particle-enhanced nephelometric immunoassay: precision, interferences, stability and reference range. Ann Clin Biochem. 2004; 41:111-118. doi: 10.1258/000456304322879980
