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Creatinine for estimation of glomerular filtration rate
S Hellerstein1, U Alon, B A Warady
1Department of Pediatrics, University of Missouri-Kansas City School of Medicine.
Pediatric Nephrology (Berlin, Germany)
|November 1, 1992
Summary
Plasma creatinine concentration and creatinine clearance overestimate glomerular filtration rate (GFR) in children. Adjusting the calculation constant (k) using inulin clearance improves GFR estimation accuracy.
Area of Science:
- Pediatric Nephrology
- Renal Physiology
Background:
- Glomerular filtration rate (GFR) is a key indicator of kidney function.
- Plasma creatinine concentration (PCr) and creatinine clearance (CCr) are commonly used to estimate GFR.
- Inulin clearance (Cin) serves as a gold standard for GFR measurement.
Purpose of the Study:
- To evaluate the accuracy of PCr and CCr in estimating GFR in children.
- To compare measured CCr and calculated CCr (calc-CCr) against Cin.
- To determine if modifying the proportionality constant (k) in GFR estimation formulas improves accuracy.
Main Methods:
- Concurrent Cin and CCr studies were conducted in 31 children (aged 5.3-20.8 years).
- GFR was measured using Cin as the reference standard.
- CCr and calc-CCr (using the formula: GFR = k.L/PCr) were compared to Cin.
Main Results:
- Measured CCr was significantly higher than Cin (16.7 +/- 10.3 ml/min/1.73 m2, P < 0.001).
- Calc-CCr also overestimated Cin (31.6 +/- 20.8 ml/min/1.73 m2, P < 0.001).
- While correlations were good (r=0.96 for Cin vs. CCr; r=0.90 for Cin vs. calc-CCr), confidence intervals were broad, indicating consistent overestimation of GFR.
Conclusions:
- Both measured and calculated CCr, using standard methods, tend to overestimate GFR in children.
- Deriving the proportionality constant 'k' from Cin (k = Cin/L) instead of CCr (k = CCr.PCr/L) offers a more accurate GFR estimation.
- This adjustment is crucial for reliable GFR assessment in pediatric populations.