Cystatin C eGFR Calculator (Adults)
Estimate glomerular filtration rate using the CKD-EPI cystatin C equation (2012), reported as mL/min/1.73m².
What is a cystatin GFR calculator?
A cystatin GFR calculator estimates kidney filtration function using blood cystatin C, age, and sex. The result is an estimated glomerular filtration rate (eGFR), usually shown in mL/min/1.73m².
Compared with creatinine-based estimates, cystatin C can be useful in cases where muscle mass, diet, or body composition might make creatinine less reliable. Many clinicians use cystatin C to confirm chronic kidney disease (CKD), clarify borderline results, or improve risk assessment.
Equation used in this calculator
This page uses the CKD-EPI cystatin C equation for adults:
- Scys = serum cystatin C in mg/L
- Age = years
- Female factor = multiply by 0.932
The formula is intended for adults and standardized lab measurements. If your lab method differs, your clinician may interpret results differently.
How to interpret your eGFR result
General GFR categories
- G1: 90 or higher (normal/high)
- G2: 60–89 (mildly decreased)
- G3a: 45–59 (mild to moderate decrease)
- G3b: 30–44 (moderate to severe decrease)
- G4: 15–29 (severely decreased)
- G5: below 15 (kidney failure range)
A single value is not enough to diagnose CKD. Diagnosis usually needs persistent abnormality over at least 3 months and/or evidence such as albuminuria.
Why cystatin C is useful
Potential advantages
- Less affected by muscle mass than creatinine.
- Helpful for older adults, very fit individuals, or people with low muscle mass.
- Can improve confidence when creatinine eGFR is borderline.
- Often used in confirmatory testing strategies.
Important limitations
- Cystatin C may be influenced by inflammation, thyroid disease, smoking, and corticosteroid use.
- Assay variation between laboratories can affect values.
- Not all populations are represented equally in equation development cohorts.
- eGFR is still an estimate; measured GFR is the reference standard when precise assessment is needed.
When to discuss results with your clinician
Contact your healthcare team if:
- Your eGFR is below 60 and this is new.
- Your eGFR drops noticeably over time.
- You have diabetes, hypertension, cardiovascular disease, or family history of kidney disease.
- You notice swelling, fatigue, foamy urine, blood in urine, or persistent changes in urination.
Your clinician may also review urine albumin-to-creatinine ratio (uACR), blood pressure, medication dose adjustments, and kidney-protective treatment plans.
FAQ
Is this calculator for children?
No. This implementation is designed for adults (age 18+).
Can I use cystatin C alone to diagnose kidney disease?
No. Diagnosis requires clinical context, repeated testing, and sometimes additional markers like uACR and imaging.
What if my cystatin eGFR and creatinine eGFR disagree?
This is common in some people. Clinicians may use combined equations, repeat testing, or prioritize the result that best fits your full medical context.
Bottom line
A cystatin GFR calculator gives a practical estimate of kidney function and can complement creatinine-based evaluation. Use it to understand trends and ask better questions at your next appointment, not as a stand-alone diagnosis.