Abstract
Glomerular filtration rate (GFR) estimated by creatinine- and/or cystatin C-based equations (eGFR) is widely used in daily practice. The purpose of our study was to compare new and old eGFR equations with measured GFR (mGFR) by iohexol clearance in a cohort of children with chronic kidney disease (CKD). We examined 96 children (median age 9.2years (range 0.25-17.5)) with CKD stages 1-5. A 7-point iohexol clearance (GFR7p) was defined as the reference method (median mGFR 66mL/min/1.73m2, range 6-153). Ten different eGFR equations, with or without body height, were evaluated: Schwartzbedside, SchwartzCKiD, SchwartzcysC, CAPA, LMREV, (LMREV + CAPA) / 2, FAScrea, FAScysC, FAScombi, FASheight. The accuracy was evaluated with percentage within 10 and 30% of GFR7p (P10 and P30). In the group with mGFR below 60mL/min/1.73m2, the SchwartzcysC equation had the lowest median bias (interquartile range; IQR) 3.27 (4.80) mL/min/1.73m2 and the highest accuracy with P10 of 44% and P30 of 85%. In the group with mGFR above 60mL/min/1.73m2, the SchwartzCKiD presented with the lowest bias 3.41 (13.1) mL/min/1.73m2 and P10 of 62% and P30 of 98%. Overall, the SchwartzcysC had the lowest bias - 1.49 (13.5) mL/min/1.73m2 and both SchwartzcysC and SchwartzCKiD showed P30 of 90%. P10 was 44 and 48%, respectively. The SchwartzcysC and the combined SchwartzCKiD present with lower bias and higher accuracy as compared to the other equations. The SchwartzcysC equation is a good height-independent alternative to the SchwartzCKiD equation in children and can be reported directly by the laboratory information system. ClinicalTrials.gov , Identifier NCT01092260, https://clinicaltrials.gov/ct2/show/NCT01092260?term=tondel&rank=2.
Highlights
5.1 Renal embryology and anatomyThe development of nephrons begins around week 9 of gestation and ceases by week 36 of gestation, with formation of 60% of the nephrons in the third trimester [1, 2]
For evaluation of glomerular filtration rate (GFR) based on natural biomarkers we recommend to use Schwartz’ estimation of GFR (eGFR)-formulas including serum cystatin C when available
Simplified measured GFR (mGFR) based on only one blood sampling after marker injection may be a practical alternative to multipoint mGFR gold standard procedures when using Fleming formula and sampling at 3 h
Summary
5.1 Renal embryology and anatomyThe development of nephrons begins around week 9 of gestation and ceases by week 36 of gestation, with formation of 60% of the nephrons in the third trimester [1, 2]. 1 million functional units called nephrons, with a range from 200.000 to >2.5 million nephrons [4, 5] These urine-producing structures span the cortex and medulla. Low birth weight (LBW), small size for gestational age (SGA) and prematurity are associated with impaired fetal nephron development, reduced glomerular surface and increased risk of hypertension and kidney disease in adult life; the Brenner hypothesis [7, 8]. There are several formulas for an approximate estimation of GFR (eGFR), based on the concentration of plasma markers or the combination of plasma and urine markers. We have performed a study to evaluate different formulas for calculating measured GFR based on plasma iohexol clearance with blood sampling at only one time point (GFR1p) and to determine the optimal sampling time point. Considerable differences within and between the different formulas were found for different CKD stages and different time points for blood sampling
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