These methods aren’t validated in a large number of patients and aren’t likely to be terribly accurate, but they are the only methods available. There are two methods to estimate “unstable” renal function (Jelliffe 1972 and Chiou 1975). Many hospitalized patients do not have a stable renal function, which means that these traditional equations are not appropriate for these patients. All traditional equations (C-G, MDRD, CKD-EPI) require that a patient have a “stable” renal function (usually two similar values drawn more than 24 hours apart). You can (roughly) estimate creatinine clearance in patients with unstable renal function.It is possible to “convert” between older methods and the newer IDMS, but this practice increases the complexity and number of corrections required to calculate a creatinine clearance. While it’s great that the assay is more accurate, older methods of estimating renal function (specifically Cockcroft-Gault) will return a lower value with IDMS than with previous assay methods. This bias can be as high as 20%, and is especially problematic with a normal creatinine (closer to 1 mg/dL). Older methods detected non-creatinine chromagens, which falsely elevated the amount of creatinine detected. Isotope Dilution Mass Spectrometry (IDMS) is the newest assay for measuring serum creatinine. CKD-EPI was designed to be as accurate as MDRD at lower renal function, but to have better precision in patients with normal renal function. In fact, the newer CKD-EPI equation was specifically developed for this problem. Because MDRD was developed in patients with renal dysfunction, it loses precision in patients with normal renal function. MDRD is not an appropriate estimation method for patients with a GFR above 60 mL/min/1.73 m 2.The best practice is probably to reduce an elderly patient’s clearance by a flat percentage (perhaps 30%), although this method hasn’t been studied. The practice is problematic because it doesn’t account for elderly patients with a creatinine above 1 mg/dL, and it doesn’t round on a percentage basis. This practice has been studied in a number of papers, and has consistently been shown to be a poor correction. In order to account for reduced muscle mass, it is a common practice for clinicians to round the serum creatinine of elderly patients to a flat 1 mg/dL. Don’t round serum creatinine to 1 mg/dL in elderly patients.Later studies have shown that the Cockcroft-Gault equation using LBW2005 (a method of estimating a patient’s lean body weight) is the most accurate method. In the original manuscript, it was shown to be more accurate than the Cockcroft-Gault and Jelliffe equations using actual body weight, which is an unfair comparator. This equation was developed in the late 1980’s for the purposes of estimating renal function in obese (BMI ≥ 30 m 2) patients. Don’t use the Salazar-Corcoran equation for obese patients. Currently, the National Kidney Foundation recommends MDRD/CKD-EPI for evaluating the progression of renal function, and C-G for dosing medications. Although the Cockcroft-Gault equation is less accurate than newer methods (MDRD and CKD-EPI) for estimating renal function, drug manufacturers typically use the older C-G method to determine renal adjustments of medications. Cockcroft-Gault is still the best equation for renally adjusting medications.The following are the top 10 facts that every clinician should know about creatinine clearance: For additional information visit Linking to and Using Content from MedlinePlus.Evaluating renal function for the purposes of drug dosing is a common task for clinical pharmacists, but a number of misconceptions have developed over the past forty years as the process of evaluating renal function has improved. Any duplication or distribution of the information contained herein is strictly prohibited without authorization. Links to other sites are provided for information only - they do not constitute endorsements of those other sites. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. This site complies with the HONcode standard for trustworthy health information: verify here. Learn more about A.D.A.M.'s editorial policy editorial process and privacy policy. is among the first to achieve this important distinction for online health information and services. follows rigorous standards of quality and accountability. is accredited by URAC, for Health Content Provider (URAC's accreditation program is an independent audit to verify that A.D.A.M.
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