Estimating glomerular filtration rate in the general population: the second Health Survey of Nord-Trondelag (HUNT II).

BACKGROUND: Guidelines recommend the modification of diet in the renal disease (MDRD) formula or the Cockcroft-Gault formula for estimating the glomerular filtration rate (GFR). However, there is an ongoing discussion whether the MDRD formula should be used in the general population as several studies have found a large underestimation of its GFR estimates. METHODS: In this study, 1,029 low-risk subjects, eligible for kidney donation according to internationally accepted criteria were selected from the population-based second Health Survey of Nord-Trondelag (HUNT II). Serum creatinine values traceable to isotope dilution mass spectrometry were used with the re-expressed MDRD formula recently published. The 2.5th, 50th and 97.5th percentiles of GFR by age were calculated and compared to reference values from the literature, which are based on GFR measured with gold standard methods in potential kidney donors. RESULTS: The difference between the 50th percentiles for MDRD estimates and measured GFR in the literature was small and constant over age: +0.5 ml/min/1.73 m(2) at age 20 and -2.0 ml/min/1.73 m(2) at age 80. Bias for Cockcroft-Gault estimates varied from 0.0 ml/min/1.73 m(2) to -21.4 ml/min/1.73 m(2). Other formulae also had a too steep age correction, and bias among the elderly varied from -10 to -30 ml/min/1.73 m(2). Hence, 30-80% of the general population above age 60 had GFR estimates below their age-specific 2.5th percentile of normal kidney function, while the MDRD formula was much more conservative (13.3%). CONCLUSION: The MDRD formula gave nearly unbiased estimates for normal GFR. All other formulae tested had, especially in the elderly, a much larger negative bias and cannot be recommended for use in the general population.