20, 21 If any correction factor is used, it is likely that a percent adjustment, similar to underweight patients, would be the most appropriate however, such a correction factor has not been studied in elderly patients. The literature does not support this practice as it often results in an underestimation of true renal function. This practice becomes even more inconsistent when an elderly patient's serum creatinine is already above 1 mg/dL. Intuitively, this practice does not make sense because rounding a serum creatinine of 0.3 mg/dL (230% increase) is much different than rounding a value of 0.8 mg/dL (25% increase). Some practitioners routinely round the serum creatinine of elderly patients (eg, > 60 years) to a value of 1 mg/dL in an effort to control for a reduced muscle mass. A newer equation, called LBW2005 19 may be a more promising estimation of lean body weight and has been derived and validated with actual patient data. This equation was not scientifically derived or validated, 15 but is extensively used in medicine. Historically, the Devine 1974 equation 18 has been used to estimate fat-free, ideal, or lean body weight (all terms generally meaning the same thing). Ideal and Lean Body Weight (Devine 1974 and LBW2005) \\ Adjusted\ weight = IdealBW + 0.4*(ActualBW-IdealBW) 17 In essence, this correction accounts for 40% of body mass above a patient's "ideal" body weight: 14 This equation is most appropriate for patients who are greater than 20-30% of their ideal body weight. The most accurate equation for creatinine clearance in obese patients is the Cockcroft-Gault equation with a 40% adjustment factor. In the process of conversion, however, the non-normalized value will also overestimate GFR in obese patients. While these may appear to circumvent the issue of obesity, these values need to be converted to a non-normalized GFR (mL/min) for the purposes of drug dosing. There are equations that report GFR as a normalized value to body surface area (mL/min/1.73 m 2).
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