Characteristics of population with normal serum creatinine impaired renal function and: The validation of a MDRD formula in a healthy general population

Background and aims: Glomerular filtration rate (GFR) provides the most accurate estimation of renal function. This study investigated the clinical characteristics of patients with impaired renal function having a normal serum creatinine level. We also validated whether the new Modification of Diet in Renal Disease (MDRD) formula can be applied in a healthy general population. Material and methods: A total 393 participants who had serum creatinine concentration below 132.6 μmol/L without underlying diseases were randomly selected on an address basis in Ansan City. According to the level of GFR, they were divided into 3 groups and we analyzed their clinical characteristics. In 75 subjects, who were randomly selected 25 cases in each group based on GFR estimated by Cockcroft-Gault (C-G) formula, true GFR was measured using the ^99mTc-DTPA renal clearance method. Results: A total 393 (male: 106, female: 287) participants were as follows: GFR < 60 ml/min/1.73 m²; 4% (n = 25); 60: ≤ GFR < 90 ml/min/1.73 m²; 26.2% (n = 103); GFR ≥ 90 ml/min/1.73 m²; 67.4% (n = 265). In the group of decreased GFR, the mean age was older (67.4 ± 10.7 vs. 48.7 ± 12.8 vs. 39.4 ± 8.2 years, p < 0.001), the gender was male (90.33 ± 28.77 vs. 110.55 ± 31.64, p < 0.001), and amount of proteinuria more increased (0.61 (0.56) vs. 0.33 (0.34) vs. 0.38 (0.33) gm/day, p = 0.007). The accuracy and precision of each formula were assessed by the difference in GFR measured by the ^99mTc-DTPA renal clearance method - estimated GFR by each formula (ΔGFR), and the coefficient of determination (r²) of different predictive equations. The results were as follows: ΔGFR = -14.78 ± 46.03, r² = 0.79 (24-hour urinary creatinine clearance), ΔGFR = -16.79 ± 57.32, r² = 0.66 (100/serum creatinine), ΔGFR = 9.54 ± 39.18, r² = 0.87 (C-G formula), ΔGFR = -12.30 ± 54.31, r² = 0.66 (AASK formula), ΔGFR = 8.70 ± 37.62, r² = 0.79 (MDRD formula). Multiple linear regression analysis and logistic regression analysis showed that age, serum creatinine, total cholesterol and 24-hour urinary protein excretion were independently related to GFR and associated with a significant increase in the risk of decrement of GFR. Conclusions: From these results, a more accurate assessment of renal function should be required in a population characterized by older age, male gender and more proteinuria. The MDRD study formula and Cockcroft-Gault formula have greater accuracy and precision with true GFR, and this equation can be applied in subjects with healthy general population.