Reporting GFR

Because chronic kidney disease (CKD) is poorly inferred from serum creatinine alone, NKDEP strongly encourages clinical laboratories to routinely estimate and report GFR when serum creatinine is measured for patients 18 and older, when appropriate and feasible. Routinely reporting eGFR with all serum creatinine determinations allows laboratories to help identify reduced kidney function for providers, thus facilitate the detection of CKD. Routine reporting is easier for some laboratories than it is for others. The following information will help laboratories appropriately report eGFR.

Common problems. Below are considerations for addressing common issues laboratories face when reporting eGFR:

• Since a patient's race is often not available to laboratories, and because mixed ethnicity can make it difficult to classify a patient's race, a general recommendation is to report the eGFR values for both African Americans and non-African Americans (See Sample eGFR Reports). This practice allows the provider to estimate the appropriate value for the patient's ethnicity. When ethnicity is known, it is acceptable to report a single eGFR appropriate for the race.
• Comments can supplement the calculated eGFR in cases where the laboratory’s information system cannot be programmed to report estimates based on race (African American or not African American). For example, if eGFR is reported based on the non-African American equation, a comment could state “For African Americans, multiply by 1.212.”
• The laboratory should exercise discretion regarding reporting multiple eGFR values when data for age or gender are not available.
• Laboratories may want to restrict eGFR reporting for some patients. In cases where information systems cannot identify patients for whom reporting eGFR is inappropriate, it is suggested that laboratories report eGFR for all patients and allow the provider to determine the suitability of a result for a patient’s condition.

Reporting Values ≥ 60mL/min/1.73m². NKDEP recommends reporting eGFR values greater than or equal to 60 mL/min/1.73 m² simply as ≥ 60 mL/min/1.73 m², and not as an exact number when using the MDRD Study equation. For values below 60 mL/min/1.73 m², the report should give the numerical estimate rounded to a whole number (e.g., "32 mL/min/1.73 m²").

There are three reasons for this recommendation:

• Interlaboratory differences in calibration of creatinine assays and the imprecision of the measurements have their greatest impact in the near-normal range and, therefore, lead to greater inaccuracies for values ≥ 60 mL/min/1.73 m² .^1, 2
• The MDRD Study equation has been most extensively evaluated in people with CKD and reduced GFR, and is less accurate for persons with normal or mildly impaired kidney function.^{2, 3, 4, 5, 6, 7, 8, 9, 10}
• Quantification of eGFR values below 60 mL/min/1.73 m² has more clinical implications for classification of kidney function than values above this level.

A laboratory that reports eGFR numeric values > 60 mL/min/1.73 m² should consider using the CKD-EPI equation. Although the CKD-EPI equation is, on average, more accurate for values > 60 mL/min/1.73 m² than is the MDRD Study equation, the influence of imprecision of creatinine assays on the uncertainty of an eGFR value is greater at higher eGFR values and should be considered when determining the highest eGFR value to report.

Sample eGFR Reports

The following sample eGFR reports were developed using the Original MDRD Study equation:

Sample eGFR report for a 63-year-old woman

• Creatinine = 1.82 mg/dL
• eGFR if African American = 36 mL/min/1.73 m²
• eGFR if non-African American = 30 mL/min/1.73 m²

Sample eGFR report for a 63-year-old woman identified as African American

• Creatinine = 1.82 mg/dL
• eGFR = 36 mL/min/1.73 m²

Sample eGFR report for a 62-year-old man

• Creatinine = 1.35 mg/dL
• eGFR if African American = ≥ 60 mL/min/1.73 m²
• eGFR if non-African American = 57 mL/min/1.73 m²

Sample eGFR report for a 55-year-old man

• Creatinine = 1.07 mg/dL
• eGFR if African American = ≥ 60 mL/min/1.73 m²
• eGFR if non-African American = ≥ 60 mL/min/1.73 m²

Note: If your printing system does not allow for superscripts, report the eGFR with mL/min/1.73 “square meters” or “m^2.” 

References

1. Myers GL, Miller WG, Coresh J, Fleming J, Greenberg N, Greene T, Hostetter T, Levey AS, Panteghini M, Welch M, Eckfeldt JH. Recommendations for improving serum creatinine measurement: a report from the laboratory working group of the National Kidney Disease Education Program. Clinical Chemistry. 2006;52:5–18.

2. Coresh J, Astor BC, McQuillan G, Kusek J, Greene T, Van Lente F, Levey AS. Calibration and random variation of the serum creatinine assay as critical elements of using equations to estimate glomerular filtration rate. American Journal of Kidney Disease. 2002;39(5):920–929.

3. Poggio ED, Wang X, Greene T, Van Lente F, Hall PM. Performance of the modification of diet in renal disease and Cockcroft-Gault equations in the estimation of GFR in health and in chronic kidney disease. Journal of the American Society of Nephrology. 2005;16(2):459–466.

4. Bostom AG, Kronenberg F, Ritz E. Predictive performance of renal function equations for patients with chronic kidney disease and normal serum creatinine levels. Journal of the American Society of Nephrology. 2002;13(8):2140–2144.

5. Vervoort G, Willems HL, Wetzels JF. Assessment of glomerular filtration rate in healthy subjects and normoalbuminuric diabetic patients: validity of a new (MDRD) prediction equation. Nephrology, Dialysis, Transplantation. 2002;17(11):1909–1913.

6. Stoves J, Lindley EJ, Barnfield MC, Burniston MT, Newstead CG. MDRD equation estimates of glomerular filtration rate in potential living kidney donors and renal transplant recipients with impaired graft function. Nephrology, Dialysis, Transplantation. 2002;17(11):2036–2037.

7. Lin J, Knight EL, Hogan ML, Singh AK. A comparison of prediction equations for estimating glomerular filtration rate in adults without kidney disease. Journal of the American Society of Nephrology. 2003;14(10):2573–2580.

8. Rule AD, Gussak HM, Pond GR, Bergstralh EJ, Stegall MD, Cosio FG, Larson TS. Measured and estimated GFR in healthy potential kidney donors. American Journal of Kidney Disease. 2004;43(1):112–119.

9. Hallan S, Asberg A, Lindberg M, Johnsen H. Validation of the Modification of Diet in Renal Disease formula for estimating GFR with special emphasis on calibration of the serum creatinine assay. American Journal of Kidney Disease. 2004;44(1):84–93.

10. Coresh J, Eknoyan G, Levey AS. Estimating the prevalence of low glomerular filtration rate requires attention to the creatinine assay calibration. Journal of the American Society of Nephrology. 2002;13(11):2811–2812.