What is the estimated glomerular filtration rate (eGFR) for creatinine clearance?

From the Guidelines

Creatinine clearance should be estimated using the MDRD study equation, which is more accurate and precise than the Cockcroft-Gault equation for persons with a GFR less than approximately 90 mL/min per 1.73 m2 1. To estimate creatinine clearance, clinicians can use prediction equations that take into account age, sex, race, and body size. The MDRD study equation is a useful tool for estimating GFR in adults, as it has been validated in a large database of patients with various kidney diseases 1. Some key points to consider when estimating creatinine clearance include:

• The MDRD study equation does not require height or weight and has been validated in kidney transplant recipients and African-Americans with nephrosclerosis 1.
• Clinicians should not use serum creatinine concentration as the sole means to assess the level of kidney function, as it is affected by factors other than GFR, such as creatinine secretion and generation and extrarenal excretion 1.
• Clinical conditions in which it may be necessary to measure GFR by using clearance methods include extremes of age and body size, severe malnutrition or obesity, diseases of skeletal muscle, paraplegia or quadriplegia, vegetarian diet, rapidly changing kidney function, and calculation of the dose of potentially toxic drugs that are excreted by the kidneys 1. The MDRD study equation is a valuable tool for estimating creatinine clearance and assessing kidney function, but it should be used in conjunction with other clinical assessments to ensure accurate diagnosis and treatment of kidney disease.

From the Research

Creatinine Clearance

• Creatinine clearance (CrCl) is a measure used to assess kidney function, particularly glomerular filtration rate (GFR) 2.
• The formula for calculating CrCl is: CrCl (mL/min/1.73m2) = (urine volume × urine creatinine × 1.73) / (serum creatinine × 30 min × body surface area) 2.
• However, studies have shown that the urinary CrCl method has poor precision for assessing GFR in critically ill patients with early acute kidney injury (AKI), with a within-group error of 55.0% 2.
• The error in estimating GFR using CrCl is high, at 103%, compared to other estimating equations such as the Cockcroft Gault (CG), the Modification of Diet in Renal Disease (MDRD), and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations 2.

Limitations of Creatinine Clearance

• The use of serum creatinine as a functional biomarker of the kidney has substantial shortcomings, including limitations in accurately interpreting creatinine values and translating them into changes in kidney function 3.
• Understanding the pathways involved in creatinine generation and metabolism, as well as the techniques involved in measuring creatinine concentrations, is critical in allowing accurate interpretation of creatinine values 3.
• Alternative functional biomarkers of the kidney may provide more accurate assessments of kidney function, but more research is needed to fully understand their value and limitations 3.

Estimating Equations

• The CG, MDRD, and CKD-EPI equations are commonly used to estimate GFR, but they perform poorly in critically ill patients with early AKI, with high biases and unacceptably high errors 2.
• The between-method bias for these equations compared to GFR measured by the infusion clearance of chromium-ethylenediaminetetraacetic acid (51Cr-EDTA) is significant, ranging from 2.6 to 11.6 ml/min 2.
• The error in estimating GFR using these equations is also high, ranging from 67.7% to 103% compared to GFR51Cr-EDTA 2.