Comparison of plasma clearance of iohexol and urinary clearance of inulin for measurement of GFR in children.

Background: Very few studies have been published that compare plasma clearance of iohexol (Cio) with renal clearance of inulin (Cin).

Study Design: Diagnostic test study.

Setting & Participants: 60 children aged 11.6 ± 4.5 years with different kidney disorders were investigated.

Index Test: Plasma Cio calculated from the slope and a single point.

Reference Test: Renal Cin with continuous infusion during water diuresis. Results were compared with the correlation coefficients, bias and precision, accuracy percentage, root mean square error, and intraclass correlation.

Other Measurements: Measured creatinine clearance and estimated glomerular filtration rate based on serum creatinine level and height.

Results: Mean Cin was 70.7 ± 41.3 (SD) mL/min/1.73 m². Mean differences between Cio and Cin were 2.65 and 2.00 mL/min/1.73 m² for the slope and single-point methods, respectively. Precision was ±16 mL/min/1.73 m² and intraclass correlation was 0.92 in both methods. Proportions of Cio within 30% of Cin were 83.3% and 86.7% for the slope and single-point methods, respectively.

Limitations: A limited number of patients; no adults were studied.

Conclusions: Plasma Cio shows good agreement with renal Cin.