GFR


Sunquest Code:CREA  
Epic Code:LAB5916Epic Name:GFR Estimated
Synonyms:Glomerular Filtration Rate, Calculation; Estimated Creatinine Clearance; GFR Calculation; eGFR
Methodology:Calculation using IDMS-traceable study equation on every serum creatinine with the following exceptions: patient is <18 years, sex unknown, or creatinine is <0.05 mg/dL.


Collection Instructions

Specimen:Blood
Container:Green (lithium heparin, gel) (Green (sodium heparin, no gel), Red (no gel), Red or gold (gel))


Processing and Shipping

Test Performed at or Referral Lab Chemistry  (Fairview Range - FRMC, UMMC-East Bank, Fairview Lakes - FLMC, Fairview Ridges - FRH, Fairview Northland - FNMC, Fairview Southdale - FSH, UMMC/UMMCH-West Bank)


Interpretive

Reference Range:

>60 mL/min/1.73m2. We suggest greater than 80 mL/min/1.73m2 as being compatible with normal renal function. Values less than 80 mL/min/1.73m2 may indicate impaired renal function, with values between 60 to 80 mL/min/1.73m2 as borderline. However, all values should be interpreted with respect to the patient’s clinical status and age. Please note that GFR declines with age in healthy people

 

 

Limitations:While the CKD-EPI estimating equation has shown modest reduction in bias with respect to measured GFR, estimated GFR (eGFR) may be imprecise in various clinical situations. Like all creatinine-based GFR estimating equations, it will suffer from physiologic limitations of creatinine as a filtration marker. 4,7  The terms for age, sex and race in the equation only captures some of the non-GFR determinants of creatinine concentration in blood. The coefficients represent average effects observed in the populations used to develop the equations.

All estimates of GFR based on serum creatinine will be less accurate for patients at the extremes of muscle mass (including frail elderly, critically ill, or cancer patients), those with unusual diets, and those with conditions associated with reduced secretion of extra-renal elimination of creatinine.

Confirmatory tests using measured GFR or measured creatinine clearance are recommended for people in whom estimates based on serum/plasma/blood creatinine alone may be inaccurate and when there is a clinical need for better accuracy in GFR determination.

Populations not well represented in the development or validation cohorts: Elderly people, and African Americans with higher levels of GFR, racial and ethnic minorities other than African Americans.

The influence of creatinine measurement imprecision at low creatinine concentrations (high eGFR) has not been carefully studied, but likely contributes to the variability at higher eGFR values.  
Use:
Glomerular filtration rate (GFR) traditionally is considered the best overall index of renal function in health and disease. The GFR is helpful for diagnosing and assessing various renal conditions. Since the GFR is difficult to measure in clinical practice, formulas have been developed to estimate GFR (eGFR).

The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation is a widely used creatinine based IDMS traceable equation for estimating GFR in patients at age 18 and over. The CKD-EPI equation includes variables for age, gender and race. By incorporating these variables, the CKD-EPI equation may allow providers to observe CKD, despite a serum creatinine concentration falling within or just above the normal reference interval. The CKD-EPI equation has shown improved accuracy for eGFR values >60 mL/min/1.73 m2 in comparison to other estimating equations.8

CKD-EPI Equation:
GFR = 141 x min (Scr/κ,1)α x max (Scr/κ,1) -1.209 x 0.993Age x 1.018 [if female] x 1.159 [if African American]

Where:
  • Scr is serum creatinine in mg/dL
  • κ is 0.7 for females and 0.9 for males
  • α is -0.329 for females and -0.411 for males
  • min indicates the minimum of Scr/κ or 1, and
  • max indicates the maximum of Scr/κ or 1.
  References:
  1. Miller WG, Myers GL, Ashwood ER, et al. Creatinine measurement:state of the art in accuracy and interlaboratory harmonization. Arch Pathol Lab Med. 2005;129:297-304.
  2. Levey AS, Stevens LA, Schmid CH, Zhang YL, Castro AF, 3rd, Feldman HI et al. A new equation to estimate golmerular filtration rate. Ann Intern Med. 2009;150(9):604-12.
  3. Stevens LA, Schmid CH, Zhang YL, Coresh J, Manzi J, Landis R et al. Development and validation of GFR-estimating equations using diabetes, transplant and weight. Nephrol Dial Transplant, 2010;25:449-57.
  4. Shemesh O, Golbetz H, Kriss JP, Myers BD. Limitations of creatinine as a filtration marker in glomerulopathic patients. Kidney Int. 1985:28(5):830-8.
  5. Perrone RD, Madias NE, Levey AS. Serum creatinine as an index or renal function: New insights into old concepts. Clin Chem. 1992;38(10):1933-53.
  6. Rule AD, Teo BW. GRF estimation in Japan and China: What accounts for the difference? Am J Kidney Dis. 2009;53(6):932-5.
  7. Rule AD Bailey KR, Schwartz GL, Khosla S, Lieske JC, Melton LJ, 3rd. For estimating creatinine clearance measuring muscle mass gives better results than those based on demographics. Kidney Int. 2009;75(10):1071-8.
  8. https://www.niddk.nih.gov/health-information/communication-programs/nkdep/laboratory-evaluation/glomerular-filtration-rate/estimating Accessed 11-12-2019.
 


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