Glomerular filtration rate via plasma iohexol disappearance: Pilot study for chronic kidney disease in children  G.J. Schwartz, S. Furth, S.R. Cole, B. Warady, A. Muñoz  Kidney International  Volume 69, Issue 11, Pages 2070-2077 (June 2006) DOI: 10.1038/sj.ki.5000385 Copyright © 2006 International Society of Nephrology Terms and Conditions

Figure 1 Iohexol disappearance curves from the blood. (a) Plot of iohexol disappearance vs time (min) on the x axis. (b) Logarithm of iohexol disappearance, showing the linear fitting of the slow (renal) curve to the points from 120 to 360 min. (c) Logarithm of iohexol disappearance, showing the linear fitting of the fast curve to the points from 10 to 60 min. This fast iohexol disappearance curve was obtained by subtracting the slow curve from the overall disappearance curve, thus revealing the linear fit of the fast curve. Kidney International 2006 69, 2070-2077DOI: (10.1038/sj.ki.5000385) Copyright © 2006 International Society of Nephrology Terms and Conditions

Figure 2 Two-component GFR comparing nine points against four points. (a) Scatterplot of GFR values computed from nine-point iohexol disappearance (x axis) vs the four-point GFR computed from samples taken at 10, 30, 120, and 300 min (y axis), with line of perfect agreement as reference, showing excellent correlation (r=0.999). (b) Bland–Altman plot of GFRs computed from the nine-point GFR (GFR(9)) vs that from the four-point GFR (GFR(4)). The agreement was excellent with no bias or trend towards changing variability at lower GFR values. Kidney International 2006 69, 2070-2077DOI: (10.1038/sj.ki.5000385) Copyright © 2006 International Society of Nephrology Terms and Conditions

Figure 3 One-component GFR. Correlation of GFR values computed from nine-point iohexol disappearance (y axis) vs GFR computed solely from the iohexol dose divided by the area under the curve of the slow (renal) component that was determined from five points between 120 and 300 min. The one-compartment model progressively underestimated GFR from the two-compartment model. Kidney International 2006 69, 2070-2077DOI: (10.1038/sj.ki.5000385) Copyright © 2006 International Society of Nephrology Terms and Conditions

Figure 4 Two-component GFR based on nine points and one component GFR based on two points (GFR(2)). (a) Regression of GFR values computed from nine-point iohexol disappearance ((GFR(9)) vs those computed from the one compartment using the coefficients for a linear and squared term determined from the curve-fitting analysis, which are similar to those used previously by Brochner-Mortensen.19 The correlation was highly significant at 0.970. (b) Bland–Altman plot of GFRs computed from the two compartment model (GFR(9)) vs that from the two-point GFR (GFR(2)). With one exception, the agreement was excellent with virtually no bias and no trend towards changing variability at lower GFR values. Kidney International 2006 69, 2070-2077DOI: (10.1038/sj.ki.5000385) Copyright © 2006 International Society of Nephrology Terms and Conditions

Figure 5 Comparison of two-compartment GFR (GFR(9)) vs estimated GFR from Schwartz formula and standard urine iohexol clearance. (a) Regression of GFR estimated from Schwartz formula (eGFR) vs two compartment GFR(9), showing an excellent correlation coefficient of 0.934. Whereas the correlation was high, the eGFR consistently overestimated GFR(9) by an average of 12.2 ml/min per 1.73 m2. The variability, while great, did not change as a function of GFR. (b) Regression of renal clearance of iohexol (urine GFR) vs the two-compartment GFR(9), showing a weaker correlation coefficient of 0.770. There appeared to be a significant amount of variability at all levels of GFR, and the renal clearance underestimated GFR(9) by 13.95 ml/min per 1.73 m2. Kidney International 2006 69, 2070-2077DOI: (10.1038/sj.ki.5000385) Copyright © 2006 International Society of Nephrology Terms and Conditions