Particularly for renally dosing medications, the Cockcroft-Gault equation has been the long-standing gold standard for the estimation of creatinine clearance for decades. The original study was based on data from male patients with stable renal function. The study used actual body weight, but mentioned that a correction factor of some kind should be used in patients with marked obesity or ascites.
Published as a "Letter to the Editor", the Jelliffe equation does not require a patient's height or weight because it describes renal function normalized to a body surface area of 1.
While this was a landmark equation for its era, its use has become deprecated in favor of newer equations. The equation is derived from a "fat free mass" equation and was shown to be superior to the Cockcroft-Gault and Jelliffe methods when using total body weight.
The MDRD equation was originally developed in 7 as a six-variable equation, but has since been updated to a simpler, four-variable equation in two variations to reflect the conventional and IDMS laboratory methods. The MDRD equation is more accurate than the Cockcroft-Gault method particularly when using total body weight , but it is rarely used for drug dosing because most medications are validated using the Cockcroft-Gault method.
Most conventional, commonly used equations to estimate renal function require that patients have a stable renal function. Unfortunately, many hospitalized patients do not have stable renal function.
For this reason, other equations have been developed to aid clinicians in estimating renal function for the purposes of drug dosing. The two most common equations for estimating unstable renal function are the Jelliffe 8 and Chiou 9 methods. Generally speaking, these equations are developed using a one-compartment pharmacokinetic estimation model, and are less accurate when renal function is improving rather than worsening.
For the purposes of drug dosing or estimating GFR in patients with body size that is very different than average, GFR can be non-normalized using the following equation: Many equations have an adjustment factor to account for the fact that female patients have less muscle mass, and therefore produce less creatinine.
Historically, the Cockcroft-Gault and Jelliffe equations used an arbitrary value of 0. Fortunately, newer data have shown that this correction factor is actually relatively accurate, with an "optimal" correction factor between 0. Obesity has been a long-standing problem in the estimation of renal function.
Creatinine Clearance Calculator
Serum creatinine production is approximated based on lean body weight because muscle tissue not fat is responsible for creatine production.
Furthermore, a change in total body mass does not increase the size of the kidney or GFR proportionally.
Equations that do not correct or adjust for obesity risk overestimation of true renal function. In one of the largest study on the topic to date of nearly overweight and obese patients, the following conclusions can be drawn: In the process of conversion, however, the non-normalized value will also overestimate GFR in obese patients.
Historically, the Devine equation 18 has been used to estimate fat-free, ideal, or lean body weight all terms generally meaning the same thing. This equation was not scientifically derived or validated, 15 but is extensively used in medicine.
A newer equation, called LBW 19 may be a more promising estimation of lean body weight and has been derived and validated with actual patient data.
Intuitively, this practice does not make sense because rounding a serum creatinine of 0. The literature does not support this practice as it often results in an underestimation of true renal function. In underweight patients, a low serum creatinine may be more reflective of a decrease in production rather than an increased rate of renal elimination.
Clearance de Creatinina
Similarly to elderly patients , clinicians may be tempted to round creatinine in underweight patients to account for less muscle mass; however, this practice is not supported by the literature. This correction factor was shown to be more precise and less bias than rounding or making no adjustment. Because serum creatinine undergoes tubular secretion, any medications that interfere with this process will falsely elevate the patient's serum creatinine; however, this will not impact the patient's true GFR.
The following medications have been shown to falsely elevate serum creatinine: 12 , 20 , Certain patient groups have dramatically different serum creatinine production or elimination compared to the normal patient population.
The following groups are notoriously difficult to estimate true renal function:. There are primarily two laboratory methods for measuring serum creatinine: a number of conventional older methods eg, alkaline picrate , and the newer IDMS method. You may specify whether you are entering serum creatinine as an IDMS or 'conventional' assay by clicking the "Config" icon in the top, right-hand corner of the page heading. Show AMA citation. IDMS is the newer, more precise method for measuring serum creatinine.
Most institutions are using IDMS by this point, but you should contacting your laboratory if you are unsure of your assay. For more information, read more about IDMS.
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Load an Example. Prediction of creatinine clearance from serum creatinine. PMID A new equation to estimate glomerular filtration rate. Ann Intern Med.
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Jelliffe RW. Letter: Creatinine clearance: bedside estimate.
Predicting creatinine clearance and renal drug clearance in obese patients from estimated fat-free body mass. Am J Med. National Kidney Foundation. Am J Kidney Dis. Using standardized serum creatinine values in the modification of diet in renal disease study equation for estimating glomerular filtration rate.
A more accurate method to estimate glomerular filtration rate from serum creatinine: a new prediction equation.
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A computer program for estimation of creatinine clearance from unstable serum creatinine levels, age, sex, and weight. Mathematical Biosciences. DOI A new simple and rapid method to monitor the renal function based on pharmacokinetic consideration of endogeneous creatinine. Res Commun Chem Pathol Pharmacol. Influence of renal function and dialysis on drug disposition.
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Chow MS, Schweizer R. Estimation of renal creatinine clearance in patients with unstable serum creatinine concentrations: comparison of multiple methods. Drug Intell Clin Pharm. Accessed December 18, Fractional adjustment of predicted creatinine clearance in females. Am J Hosp Pharm.
Impact of various body weights and serum creatinine concentrations on the bias and accuracy of the Cockcroft-Gault equation. The origin of the "ideal" body weight equations.
Ann Pharmacother. Estimation of creatinine clearance in morbidly obese patients. Am J Health Syst Pharm. Experience with a once-daily aminoglycoside program administered to 2, adult patients. Antimicrob Agents Chemother. Devine BJ. Gentamicin therapy. Quantification of lean bodyweight. Clin Pharmacokinet. Estimating creatinine clearance in elderly patients with low serum creatinine concentrations. Estimating aminoglycoside dosage requirements in patients with low serum creatinine concentrations.
Estimating aminoglycoside clearance and creatinine clearance in underweight patients.
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Estimation of creatinine clearance in malnourished patients. Clin Pharm. Estimating glomerular filtration rate with a modification of diet in renal disease equation: implications for pharmacy. National Kidney Disease Education Program.
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