Test Details
Estimated Glomerular Filtration Rate (eGFR) / Cystatin C
Estimated glomerular filtration rate (eGFR) / Cystatin C is automatically calculated when serum cystatin C is ordered. It provides a measure of kidney filtering capacity. Total GFR can be used as an index of functioning renal mass. eGFR using cystatin C performs significantly better in prediction models than eGFR calculated from creatinine. Serum cystatin C and age are used to calculate eGFR, taking sex into account.
Methodology
Serum cystatin C and age are used to calculate eGFR, taking age and sex into account. The specific equation used is:
When serum Cystatin C is <0.8 mg/L:
Male: eGFR (Cystatin C) = 133 x (Cystatin C/0.8)-0.499 x 0.996Age
Female: eGFR (Cystatin C) = 133 x (Cystatin C/0.8)-0.499 x 0.996Age x 0.932
When serum Cystatin C is >0.8 mg/L:
Male: eGFR (Cystatin C) = 133 x (Cystatin C/0.8)-1.328 x 0.996Age
Female: eGFR (Cystatin C) = 133 x (Cystatin C/0.8) -1.328 x 0.996Age x 0.932
Patient Preparation
None
Preferred Specimen
N/A
Alternate Specimen
N/A
Transport Temperature
N/A
Stability
N/A
Lab Values
Estimated Glomerular Filtration Rate (eGFR) / Cystatin C
- Optimal: >60 mL/min/1.73 m2
- Borderline: 30-60 mL/min/1.73 m2
- Increased Risk: <30 mL/min/1.73 m2
Clinical Significance
Estimated Glomerular Filtration Rate (eGFR) / Cystatin C
- Low or decreasing eGFR is an indicator of chronic kidney disease (CKD).
- Monitoring changes in eGFR can delineate progression of kidney disease.
- The level of GFR is a strong predictor of the time to onset of kidney failure as well as the risk of complications of CKD.
- Monitoring eGFR allows proper dosing of drugs excreted by glomerular filtration to avoid drug toxicity.
Treatment Options
Estimated Glomerular Filtration Rate (eGFR) / Cystatin C
- Treatment is based on the cause of the renal dysfunction.
- Patients with low and borderline levels are at increased risk of kidney failure. Both groups need to have their diabetes and hypertension carefully controlled, if present.
