The curve uses the same equation and updates with your inputs. A marker appears after calculation.
Example Data Table
| Age | Sex | Cystatin C (mg/L) | eGFR (mL/min/1.73 m²) | Category |
|---|---|---|---|---|
| 45 | Female | 0.90 | 88.5 | G2 |
| 65 | Male | 1.10 | 67.1 | G2 |
| 72 | Female | 1.60 | 37.0 | G3b |
| 38 | Male | 0.75 | 117.9 | G1 |
| 58 | Female | 1.30 | 51.6 | G3a |
Examples are illustrative only and not medical advice.
Formula Used
This calculator uses the CKD-EPI 2012 cystatin C equation (standardized cystatin C in mg/L). It estimates GFR normalized to 1.73 m² of body surface area.
Optional body-size adjustment uses Du Bois BSA: BSA = 0.007184 × Height0.725 × Weight0.425, then Absolute GFR = eGFR × (BSA / 1.73).
How to Use This Calculator
- Enter the measured cystatin C value and select its unit.
- Enter age and select sex to apply the correct factor.
- Optionally add height and weight for absolute (de-indexed) GFR.
- Choose rounding, then press Calculate.
- Use CSV or PDF buttons to export the displayed results.
If you are feeling unwell, have swelling, reduced urine output, or very high creatinine, seek urgent medical care.
What cystatin C represents
Cystatin C is a 13 kDa protein produced by most nucleated cells and released into blood at a steady rate. Laboratories report it in mg/L; some reports use mg/dL, where 1 mg/dL equals 10 mg/L. It is filtered by the glomerulus and reabsorbed in tubules, so rising values indicate lower filtration.
How the calculator estimates eGFR
The CKD-EPI 2012 cystatin C equation scales cystatin C to a pivot of 0.8 mg/L. It uses two power terms: min(Scys/0.8,1)^−0.499 for values below 0.8, and max(Scys/0.8,1)^−1.328 for values above 0.8. Age reduces eGFR by 0.4% per year via 0.996^Age, and sex applies a 0.932 multiplier for females.
eGFR categories used on screen
Results are reported as mL/min/1.73 m², indexed to a standard body surface area. The category badge follows KDIGO G stages: G1 ≥90, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29, and G5 <15. These ranges help summarize risk, but diagnosis also depends on duration and urine findings.
Why cystatin C is a useful marker
Creatinine can be influenced by muscle mass, diet, and certain medications. Cystatin C may improve estimation when creatinine seems discordant or when confirmation is needed near decision thresholds. Some guidance suggests confirming chronic kidney disease when creatinine eGFR is 45–59 with urine albumin-to-creatinine ratio below 30 mg/g, using an additional marker such as cystatin C.
Optional body-size adjustment
Indexed eGFR assumes 1.73 m². If you enter height and weight, the tool calculates Du Bois BSA: 0.007184 × Height^0.725 × Weight^0.425. It then de-indexes to an absolute GFR using eGFR × (BSA/1.73). For example, BSA 2.00 m² scales results by about 1.16.
Using outputs for trend tracking
Single results can vary with hydration, inflammation, and assay differences, so trends are more informative than one number. Export CSV for spreadsheets or PDF for clinic notes, keeping the same unit choice and rounding each time. Recheck abnormal values and discuss medication dosing, imaging contrast, and follow-up timing with a clinician.
FAQs
1) Which unit should I choose for cystatin C?
Use the unit from your lab report. Most labs report mg/L. If your report is mg/dL, select mg/dL; the tool converts using 1 mg/dL = 10 mg/L before calculating.
2) Is this calculator intended for children?
No. The equation implemented here is commonly applied to adults (18+). Pediatric kidney function estimation uses different equations and reference standards, so use a child-specific calculator and clinical guidance.
3) Why does eGFR decrease as age increases?
The equation includes an age term (0.996^Age), which reduces the estimate by about 0.4% per year. This reflects population-level differences and helps align estimates with measured GFR distributions.
4) What is “absolute” or de-indexed GFR?
Standard eGFR is normalized to 1.73 m² body surface area. If you enter height and weight, the tool estimates your BSA and converts eGFR to an absolute mL/min value using eGFR × (BSA/1.73).
5) Can I use the result for medication dosing?
Medication dosing rules vary and may use creatinine-based estimates, absolute GFR, or measured clearance. Use this output as supportive information and confirm dosing decisions with a clinician or pharmacist and local protocols.
6) What if I’m acutely ill or dehydrated?
During acute illness, kidney function can change quickly and eGFR equations may be less reliable. If symptoms are severe or results are markedly abnormal, seek urgent medical care and repeat testing as advised.