From the Guidelines
The creatinine clearance rate should be determined using the Cockcroft-Gault formula, which requires the patient's serum creatinine level, age, weight, and gender, as it provides a superior estimate of renal function compared to serum creatinine alone 1. To calculate the creatinine clearance rate using the Cockcroft-Gault formula, multiply (140 minus age) by weight in kilograms, then divide by 72 times serum creatinine; for females, multiply the result by 0.85. Some key points to consider when determining creatinine clearance rate include:
- The Cockcroft-Gault formula is the most commonly used method for estimating creatinine clearance rate 1
- The formula has been shown to provide a more accurate estimate of renal function than serum creatinine alone, especially in patients with renal insufficiency 1
- However, the formula may not be reliable for obese or edematous patients, and may underestimate GFR in patients with normal or moderately reduced renal function 1
- A 24-hour urine collection can be performed for more accurate results, but this method is not always practical in daily clinical practice 1
- The National Kidney Foundation recommends using a prediction equation, such as the Cockcroft-Gault formula, to estimate GFR in addition to reporting serum creatinine measurement 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
From the Research
Determining Creatinine Clearance Rate
To determine the creatinine clearance rate, several methods can be used, including:
- The Cockcroft-Gault equation, which estimates creatinine clearance based on serum creatinine, age, weight, and sex 2, 3
- The Modification of Diet in Renal Disease (MDRD) equation, which estimates glomerular filtration rate (GFR) based on serum creatinine, age, sex, and race 4
- The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, which estimates GFR based on serum creatinine, age, sex, and race 5, 6, 4
- The 24-hour urine collection for creatinine clearance evaluation, which is considered the gold standard for measuring GFR 4
Factors Affecting Creatinine Clearance Rate
Several factors can affect the accuracy of creatinine clearance rate estimates, including:
- Age: Older adults may have decreased renal function, which can affect creatinine clearance rate estimates 2, 3
- Weight: Low body weight can be a predictor of dosing errors in elderly patients 3
- Sex: Female patients may have lower creatinine clearance rates than male patients 2
- Race: The use of race in estimating GFR has been controversial, and some equations have been developed to be race-free 6
- Comorbid conditions: Patients with significant comorbid conditions may have decreased renal function, which can affect creatinine clearance rate estimates 5
Choosing the Best Method
The choice of method for determining creatinine clearance rate depends on the individual patient and the clinical setting. The CKD-EPI equation is recommended for estimating GFR in adults with stable kidney function 6, while the MDRD equation may be more accurate in certain populations 4. The Cockcroft-Gault equation is still widely used, but its accuracy may be limited in certain populations 5, 3. Ultimately, the best method for determining creatinine clearance rate will depend on the individual patient's characteristics and the clinical context. 5, 2, 6, 4, 3