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Validity of endogenous creatinine clearance in low birthweight infants
Insights
Endogenous creatinine clearance is a useful estimate of glomerular filtration rate (GFR) in low birthweight infants. However, it may overestimate GFR at lower levels and underestimate it at higher levels.
Area of Science:
- Neonatal physiology
- Renal function assessment
Background:
- Endogenous creatinine clearance is frequently used to estimate glomerular filtration rate (GFR).
- Its validity in low birthweight infants, a vulnerable population, requires careful evaluation.
Purpose of the Study:
- To compare inulin clearance with endogenous creatinine clearance in low birthweight infants.
- To establish the accuracy of creatinine clearance as a GFR estimation in this cohort.
Main Methods:
- Simultaneous measurement of GFR using inulin and endogenous creatinine clearances.
- Study conducted on 33 low birthweight infants (mean birthweight 1600g, mean gestational age 33 weeks) within 10 days of birth.
Main Results:
- A direct correlation was observed between inulin and creatinine clearances (r=0.738, P<0.001).
- Creatinine clearance overestimated GFR in the low GFR range and underestimated it in the high GFR range.
- The ratio of creatinine to inulin clearance was significantly higher in the low GFR group (1.28 vs. 0.89, P<0.05).
Conclusions:
- Endogenous creatinine clearance provides a reasonable estimation of GFR in low birthweight infants.
- Adjustments may be necessary for accurate GFR assessment, particularly at the extremes of renal function.
Abstract:
Despite methodologic problems, endogenous creatinine clearance is commonly used as an estimation of glomerular filtration rate (GFR). Inulin clearance was compared to endogenous creatinine clearance in a group of low birthweight infants to establish the validity of the latter. Thirty-three low birthweight infants (birthweight mean = 1600 g, gestational age mean = 33 wk) were studied between 10 hr and 10 days of age to simultaneously measure GFR by inulin and endogenous creatinine clearances. Inulin and creatinine clearances correlated directly (r = 0.738, P greater than 0.001). The slope of the regression line suggested an overestimation of GFR (inulin clearance) by creatinine clearance at the low GFR range and an underestimation at the high GFR range. The data were divided into two groups by the median inulin clearance (12.5 ml/min/1.73m2). The ratio of creatinine to inulin clearance was significantly higher in the low GFR group (1.28 +/- 0.16 vs. 0.89 +/- 0.04 SEM, n = 19, P less than 0.05). There was no difference between the two groups in plasma creatinine, birthweight, gestational age, incidence of respiratory distress, or oxygen requirements at the time of the studies. Endogenous creatinine clearance represents a good estimation of GFR (inulin clearance) in low birthweight infants. However, at the low GFR range, it represents an overestimation and at the high GFR range, an underestimation.