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GFR ≈ CrCl: Approximation of GFR from measured creatinine clearance, though not exact; often used interchangeably in practice.
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GFR (Glomerular Filtration Rate) is often approximated using measured creatinine clearance (CrCl) values. While not identical, CrCl provides a practical estimate of GFR in clinical practice and is commonly used interchangeably, especially when direct GFR measurement is not available.
The calculator uses direct approximation:
Where:
Explanation: This approximation assumes that creatinine clearance provides a reasonable estimate of glomerular filtration rate, though in reality GFR is typically slightly lower than CrCl due to tubular creatinine secretion.
Details: Accurate GFR estimation is essential for assessing kidney function, diagnosing chronic kidney disease, determining appropriate medication dosages, and monitoring disease progression over time.
Tips: Enter the measured creatinine clearance value in mL/min. Ensure the value represents a properly collected 24-hour urine sample or timed collection for accurate results.
Q1: How accurate is this approximation?
A: While useful for clinical estimation, GFR is typically 10-20% lower than CrCl due to tubular secretion of creatinine. For precise assessment, direct GFR measurement methods are preferred.
Q2: When is this approximation most useful?
A: This approximation is particularly useful when only creatinine clearance data is available from 24-hour urine collections, or for quick clinical assessments where precise GFR measurement is not feasible.
Q3: What are the limitations of using CrCl as GFR?
A: Limitations include overestimation due to tubular creatinine secretion, variability in urine collection completeness, and influence by dietary meat intake and muscle mass.
Q4: How does this compare to estimated GFR equations?
A: Estimated equations (CKD-EPI, MDRD) use serum creatinine and demographic factors, while this method uses measured urine creatinine clearance. Each has different applications and limitations.
Q5: When should direct GFR measurement be used instead?
A: Direct measurement (iohexol, iothalamate clearance) should be considered for drug dosing in critical situations, evaluation for kidney donation, or when estimated methods provide conflicting results.