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There are doubts about whether the values obtained from the Cockroft-Gault (Cl_{CG}) and Modification of Diet in Renal Disease (GFR_{MDRD}) formulas are comparable to the more traditional formula used to obtain the creatinine clearance from a 24-hour urine collection (ClCr_{m}), particularly in patients with only one kidney. The present study aimed to compare these formulas in individuals with one remaining kidney after previous nephrectomy (Nx) and to verify which estimated formula correlates more closely with ClCr_{m}. Thirty-six patients who had undergone Nx had their renal filtration analyzed with Cl_{CG}, GFR_{MDRD} and by ClCr_{m}. The average time after Nx was ^{2} for ClCr_{m}, ^{2} for ClCr_{CG}, and ^{2} for GFR_{MDRD} (with ClCr_{m} > ClCr_{CG} and GFR_{MDRD}; _{CG} and GFR_{MDRD} values (_{m}, although ClCr_{CG} was more closely associated with ClCr_{m} than GFR_{MDRD} (ClCr_{CG} with _{MDRD} with _{CG} is more related to the values obtained with the traditional clearance measurement based on a 24-hour urine collection test.

The Kidney Disease Outcomes Quality Initiative guidelines from the National Kidney Foundation classify stages of Chronic Kidney Disease according to the estimated glomerular filtration rate (GFR), which is considered the best index of function in both healthy and diseased kidneys [

Numerous formulas have been developed to estimate GFR or creatinine clearance from serum creatinine and other sources. One widely used formula for predicting creatinine clearance was proposed by Cockcroft and Gault Gault. More recently, the Modification of Diet in Renal Disease (MDRD) study formula, which uses four or six variable equations, has been used to evaluate GFR in clinical practice. However, there are concerns about whether the values obtained from the CG and MDRD formulas are comparable to the measured creatinine clearance values obtained traditionally from a 24-hour urine collection test, particularly in patients with only one kidney. The present study aimed to compare these formulas with measured GFRs in individuals with one kidney remaining after unilateral nephrectomy.

In this cross-sectional study, thirty-six individuals who underwent unilateral nephrectomy were enrolled. The mean age was _{m}) and ClCr by the Cockcroft-Gault formula (ClCr_{CG}) and by the MDRD formula (GFR_{MDRD}). The value obtained for serum creatinine on day 1 was used to calculate the ClCr_{m}, ClCr_{CG}, and GFR_{MDRD}. The same was performed for day 2. Because all measurements and formulas were conducted in duplicate (on day 1 and day 2) for each individual, a total of 72 results were obtained for each clearance. The abbreviated GFR_{MDRD} was calculated with the following formula: 175 × plasma creatinine^{−1.154} × age^{−0.203} (× 0.742 if female; × 1.21 if black) [_{CG} was calculated with the following formula: (140 – age) × body weight/plasma creatinine × 72 (× 0.85 for females) [^{2}).

Characteristics of the studied population (

Male gender ( | 11 (30.5) |

Black race ( | 14 (38) |

Age (years; mean ± SD, range) | 50.7 ± 10.6 (29–79) |

Time after nephrectomy (years; mean ± SD, range) | 11.6 ± 9.0 (2 m–38 y) |

Body weight (kg; mean ± SD, range) | 72.8 ± 16.4 (43–119) |

BSA (m^{2}; mean ± SD, range) | 1.74 ± 0.22 (1.27–2.24) |

Plasma creatinine (mg/dL; mean ± SD, range) | 1.3 ± 0.67 (0.8–4.1) |

Plasma creatinine >2 mg% ( | 3 (8.3%) |

Measured creatinine clearance: | |

First day (mL·min·m^{2}) | 79.8 ± 4.4 |

Second day (mL·min·m^{2}) | 81.6 ± 4.4 |

BSA: Body surface area; first versus second day (

All values were evaluated for normality using D’Agostinho and Pearson tests. If a Gaussian distribution was confirmed, ANOVA and Tukey post tests were applied. Linear regression was calculated between the variables. The slopes of each curve were compared for equality using the

The participants’ clinical characteristics are shown in Table ^{2} for ClCr_{m}, ^{2} for ClCr_{CG}, and ^{2} for GFR_{MDRD} (Figure _{m} versus CrCl_{CG} (_{m} versus GFR_{MDRD} (_{MDRD} and CrCl_{CG} were similar (_{m} and CLCr_{CG} was positive and significant (_{m} and GFR_{MDRD} was positive and significant (_{CG} (0.4456 to 0.6375) was compared with the slope of GFR_{MDRD} (0.2247 to 0.4305) in relation to ClCr_{m}, different values were obtained (

A comparison of the measured (ClCr_{m}) and estimated (ClCr_{CG}) creatinine clearances and glomerular filtration rate (GFR_{MDRD}) in patients with a single kidney.

The correlation between measured (ClCr_{m}) and estimated (CLCr_{CG}) creatinine clearances in patients with a single kidney.

The correlation between measured creatinine clearance (ClCr_{m}) and the estimated GFR_{MDRD} formula in patients with a single kidney.

The ClCr_{CG} and GFR_{MDRD} slopes in relation to measured creatinine clearance (CLCr_{m}).

The most commonly used formulas to calculate creatinine clearance and glomerular filtration rate are the Cockcroft-Gault and Modification of Diet in Renal Disease formulas, which tend to underestimate renal function by approximately 25% to 30% at its upper limit in normal individuals as well as patients with CKD [_{m}, ClCl_{CG}, and GFR_{MDRD} for the same patient using the same serum creatinine values. This work is not aimed to establish the clearance measured by 24-hour urine collection as the gold standard because, as described above, this method has inherent errors. Rather, we aimed to determine which of the formulas produces results closest to those obtained via the traditional method (i.e., 24-hour urine collection) in patients with a single kidney.

The results of this study showed that the estimated clearance values (ClCr_{CG} and GFR_{MDRD}) in single-kidney patients were not different from each other, but both differed from the ClCr_{m} (on the order of −5% for ClCr_{CG} and −4% for GFR_{MDRD}) (Figure _{m}, we observed significant correlations between ClCr_{CG} (Figure _{MDRD} (Figure _{CG} was larger than the _{MDRD}. Accordingly, for the same creatinine levels and the same patient, the ClCr_{CG} was more strongly correlated with CLCr_{m} than with GFR_{MDRD} (0.67 versus 0.34;

In Figure _{m} both in hyper- and in hypofiltration (slope 0.4 to 0.6; _{MDRD} distances itself more from CICr_{m} in any situation (slope 0.2 to 0.4; ^{2}) evidencing that from this point on there are distinct modifications in the estimated values in relation to the measured clearance values. Both the ClCr_{CG} and the GFR_{MDRD}, if they are over 90 mL·min·m^{2}, they underestimate the values in relation to the CICr_{m}, and if they are under that, they overestimate them in relation to the values of the CICr_{m}. It was possible to conclude that CICr_{CG} is the estimate formula that most closely matches the CICr_{m}. It should be noted that our data included a large range of values for age, BSA, and time after nephrectomy (Table