Reporting Glomerular Filtration Rate

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 facilitating 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, for the MDRD equation, or 1.159 for the CKD-EPI equation.”
  • 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. In general, 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. 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
  • All estimating equations are 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 use the CKD-EPI equation, because the CKD-EPI equation is more accurate for values > 60 mL/min/1.73 m2 than is the MDRD Study equation. However, 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 IDMS traceable MDRD Study equation:

Sample eGFR report for a 63-year-old woman

  • Creatinine = 1.82 mg/dL
  • eGFR if African American = 34 mL/min/1.73 m2
  • eGFR if non-African American = 28 mL/min/1.73 m2

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

  • Creatinine = 1.82 mg/dL
  • eGFR = 34 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 = 54 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