CREATININE-CYSTATIN C-BASED CKID EQUATION

eGFR =
39.8 x [ht/Scr]^0.456 x [1.8/cysC]^0.418 x [30/BUN]^0.079 x [1.076^male] [1.00^female] x [ht/1.4]^0.179

Abbreviations / Units

eGFR (estimated glomerular filtration rate) = mL/min/1.73 m²

BUN (blood urea nitrogten) = mg/dL

cysC (cystatin C) = mg/L

ht (height) = meters

Scr (standardized serum creatinine) = mg/dL

Assays

The cystatin C value is not yet standardized to IFCC standards. As a result, it may overestimate true GFR. It utilizes the Siemans (Date Behring) method for cystatin C.
To learn more, go to http://ckdepi.org/assays/cystatin-c/ or http://nkdep.nih.gov/lab-evaluation/cystatin-c.shtml.
Creatinine is assayed using methods that are traceable to IDMS assigned NIST certified reference materials. To learn more, go to nkdep.nih.gov.

Clinical Use

For use in children 1-18 years old.
May be useful as a confirmatory test in specific circumstances when eGFR based on serum creatinine is less accurate, or when the clinical scenario warrants a secondary test.
In most cases, the Bedside Schwartz equation [0.413(ht/cm/Scr)] allows rapid and reasonably accurate estimation of GFR for clinical use in children with CKD. When measurement and calibration is more broadly available, GFR estimates using cystatin C may also have broad clinical utility.

References

Schwartz GJ, Schneider MF, Maier PS, et al. Improved equations estimating GFR in children with chronic kidney disease using an immunonephelometric determination of cystatin C. Kidney Int. 2012;82(4):445-453.
Grubb A, Blirup-Jensen S, Lindstrom V, Schmidt C, Althaus H, Zegers I. First certified reference material for cystatin C in human serum ERM-DA471/IFCC. Clin Chem Lab Med. 2010;48(11):1619-1621.