Age-dependent reference intervals for estimated and measured glomerular filtration rate

Abstract

Background: Defining mean and reference intervals for glomerular filtration rate (GFR) has been the subject of only a limited number of studies and review articles, with contradicting statements about the mean. Normal measured GFR (mGFR) values of ∼120-130 mL/min/1.73 m² have long been the referenced values for young adults but seem to be too high according to recent studies. Reference intervals are difficult to define because of the age decline of GFR, which is also observed in healthy subjects. Little data are available for subjects >70 years of age.

Methods: Based on the reference intervals for serum creatinine (SCr) and the recently published full-age spectrum (FAS) equation, we define simple age-dependent equations for the reference limits of GFR. The mGFR of 633 living potential kidney donors was used to validate the new formulae that define the reference interval.

Results: The reference limits for estimated GFR (eGFR), calculated by entering the reference limits for SCr into the FAS equation closely correspond with published reference limits for mGFR. Of the mGFRs of potential living kidney donors, 97.2% lie between the newly defined reference limits for GFR.

Conclusion: SCr reference limits may serve to define age-dependent reference limits for eGFR and mGFR.

Keywords: age-dependent reference intervals; estimated and measured glomerular filtration rate.

Fig. 1

Box plot for mGFR versus age decades for female (filled circles) and male (filled triangles) potential kidney donors (n = 633). A horizontal reference line is drawn at GFR = 107.3 mL/min/1.73 m².

Fig. 2

Potential (healthy) kideny donors: n = 633 [550, Lyon, France (solid gray circles); 41, Liège, Belgium (open squares); 42, Leuven, Belgium (solid black circles)]. Of mGFR values, 97.2% lie between the upper and lower limit defined by the FAS equation with SCr/Q = 1.33 and SCr/Q = 0.67, respectively (upper and lower solid lines). Of mGFR values, 91.8% lie between the symmetrical upper and lower eGFR limit (lower solid line and dashed line). The middle solid line corresponds with SCr/Q = 1, the average FAS prediction for GFR.

Fig. 3

Upper and lower limits (solid circles) calculated from the meta-analysis data [6] with error bars (= 2 SD) (Table 2). The solid lines are calculated from the FAS equation with SCr/Q = 1.33 (lower limit) and SCr/Q = 0.67 (upper limit). The dashed line is calculated as mean FAS + ΔFAS.