How To Calculate Creatinine Clearance From eGFR

Creatinine Clearance Formula:

\[ CrCl \approx eGFR \times \left( \frac{BSA}{1.73} \right) \]

Creatinine Clearance (CrCl):

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1. What Is Creatinine Clearance?

Creatinine clearance (CrCl) measures the volume of blood plasma cleared of creatinine per unit time. It provides a more accurate assessment of kidney function for drug dosing and clinical decision-making compared to eGFR alone.

2. How To Calculate CrCl From eGFR?

The calculator uses the conversion formula:

\[ CrCl \approx eGFR \times \left( \frac{BSA}{1.73} \right) \]

Where:

\( CrCl \) — Creatinine clearance (mL/min)
\( eGFR \) — Estimated glomerular filtration rate (mL/min/1.73m²)
\( BSA \) — Body surface area (m²)
\( 1.73 \) — Standard body surface area reference

Explanation: This formula adjusts the eGFR (normalized to standard BSA) to the individual's actual body surface area, providing a more personalized creatinine clearance value.

3. Importance Of Creatinine Clearance

Details: Creatinine clearance is essential for accurate drug dosing of renally excreted medications, assessing true kidney function in patients with unusual body habitus, and guiding clinical decisions in special populations.

4. Using The Calculator

Tips: Enter eGFR in mL/min/1.73m² and body surface area in m². BSA can be calculated using various formulas (Mosteller, Du Bois, etc.). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why convert eGFR to CrCl?
A: eGFR is normalized to standard body surface area, while CrCl provides the actual clearance rate for the individual, which is crucial for drug dosing.

Q2: How accurate is this conversion?
A: This provides a good estimate, but measured CrCl (24-hour urine collection) may be more accurate in specific clinical situations.

Q3: When is this conversion most useful?
A: Particularly important for drug dosing in patients with very small or large body size, and for medications with narrow therapeutic windows.

Q4: What are normal CrCl values?
A: Normal CrCl is approximately 95-125 mL/min for young adults, declining with age. Values below 60 mL/min indicate impaired kidney function.

Q5: Are there limitations to this method?
A: Less accurate in patients with rapidly changing kidney function, muscle wasting, or those with non-steady-state creatinine levels.