GFR RESOURCE PAGE

CYSTATIN GFR

Serum creatinine has a drawback in the measurement of glomerular filtration rate (GFR) in that it may vary according to muscle mass. Cystatin C is a 13 kilodalton protein that is filtered by the glomerulus and reabsorbed and metabolized by tubular cells. The amount that is excreted into the urine is negligible. Its production is very steady, and not dependent on muscle mass. It has been proposed as an alterate marker Ifor estimating GFR. (coresh)

The literature is emerging, and showing that it has a benefit as a marker. Here are two formulae that might be useful in demonstrating the relationships between serum creatinine and serum cystatin C in adults. A Pediatric Cystatin GFR has been evaluated by Schwartz, et al (5)

CYSTATIN FORMULA

DADE NEPHELOMETRY ADULT GFR = 77.24 X cys -1.2623
DAKO TURBIDOMETRY ADULT GFR =99.43 X cys -1.5837

SCHWARTZ CKiD PEDIATRIC FORMULA:

GFR (ml/min per 1.73 m2)=39.1[height (m)/Scr (mg/dl)]0.516 * [1.8/cys (mg/L)]0.294[30/BUN (mg/dl)]0.169[1.099]male[height (m)/1.4]0.188.

cys = serum cystatin c (in mg/L)

REDSIDE SCHWARTZ EQUATION (CREATININE):

0.413*height(cm)/Scr(mg/dL)

COUNAHAN-BARRATT EQUATION (CREATININE)

0.43*height(cm)/Scr(mg/dL)

WHAT DOES "TRACEABLE TO IDMS" MEAN?

To properly measure theGFR one must accurately measure the serum creatinine. When a laboratory calibrates their method to the single standardized serum creatinine using reference materials traceable to the primary reference material at the National Institute of Standards, we say that value is traceable to IDMS because the test is based on isotope dilution mass spectrometry (IDMS).


REFERENCES

  1. Dade-Behring Assay from Siemens
  2. Dako Control set
  3. Stevens LA, Padala S, Levey AS. Advances in glomerular filtration rate-estimating equations. Curr Opin Nephrol Hypertens. 2010 May;19(3):298-307.
  4. Expressing the Modification of Diet in Renal Disease Study Equation for Estimating Glomerular Filtration Rate with Standardized Serum Creatinine Values. Clin. Chem, 2007 Apr;53(4):766-72.
    5. .
  5. Stevens LA, Coresh J, Schmid CH, Feldman HI, Froissart M, Kusek J, Rossert J, Van Lente F, Bruce RD 3rd, Zhang YL, Greene T, Levey AS. Estimating GFR using serum cystatin C alone and in combination with serum creatinine: a pooled analysis of 3,418 individuals with CKD. Am J Kidney Dis. 2008 Mar;51(3):395-406
  6. Cystatin Children's GFR Calculator
  7. Schwartz, GJ, Munoz, A, Schneider, MF, Mak, RH, Kaskel, F, Warady, BA & Furth, SL: New Equations to Estimate GFR in Children with CKD. J Am Soc Nephrol:ASN.2008030287, 2009.
  8. Larsson A, Malm J, Grubb A, Hansson LO. Calculation of glomerular filtration rate expressed in mL/min from plasma cystatin C values in mg/L. Scand J Clin Lab Invest. 2004;64(1):25-30.
  9. Menon V, Shlipak MG, Wang X, Coresh J, Greene T, Stevens L, Kusek JW, Beck GJ, Collins AJ, Levey AS, Sarnak MJ Cystatin C as a risk factor for outcomes in chronic kidney disease.Ann Intern Med. 2007 Jul 3;147(1):19-27.