Discordance Between Iothalamate and Iohexol Urinary Clearances
Jesse C Seegmiller1, Bradley E Burns2, Carrie A Schinstock3
1Department of Laboratory Medicine, University of Minnesota, Rochester, MN.
Background:
Iothalamate and iohexol are contrast agents that have supplanted inulin for the measurement of glomerular filtration rate (GFR) in clinical practice. Previous studies have noted possible differences in renal handling of these 2 agents, but clarity about the differences has been lacking.
Study Design:
Study of diagnostic test accuracy.
Setting & Participants:
150 participants with a wide range of GFRs were studied in an outpatient clinical laboratory facility.
Index Tests:
Simultaneous urinary clearances of iothalamate, iohexol, and creatinine.
Reference Test:
None.
Outcome:
Relative differences between the urinary clearances. Iohexol and iothalamate in plasma and urine were assayed concurrently by a novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay.
Results:
Mean iohexol, iothalamate, and creatinine clearances were 52±28 (SD), 60±34, and 74±40 mL/min/1.73 m(2), respectively. The proportional bias of iohexol to iothalamate urinary clearance was 0.85 (95% CI, 0.83-0.88) and was proportional across the GFR range. The mean proportional bias of iohexol clearance compared with creatinine clearance is 1.27 (95% CI, 1.20-1.34), whereas that of iothalamate clearance compared with creatinine clearance is 1.09 (95% CI, 1.03-1.15).
Limitations:
Lack of reference standard.
Conclusions:
This study reveals a significant and consistent difference between urinary clearances of iothalamate and iohexol. Comparison of studies reporting renal clearance measurements using iohexol versus iothalamate must account for this observed bias.
More Related Videos
Related Concept Videos
Hepatic Drug Clearance: Restrictive and Nonrestrictive Clearance
Most drugs undergo restrictive clearance, which is proportional to the...
One-Compartment Open Model for IV Bolus Administration: Estimation of Clearance
In the one-compartment open model for intravenous (IV) bolus administration, clearance is estimated by dividing the elimination rate by the plasma drug concentration. This equation leverages the elimination rate constant and the apparent...
Renal Drug Clearance: Comparison Between Renal Excretion Methods
Renal clearance is often associated with the renal glomerular filtration rate (GFR), which represents the rate at which plasma is filtered through the glomeruli in the kidney. When drug reabsorption is minimal and there is no active secretion, renal clearance is closely related to the...
Drug Elimination: The Concept of Clearance
Drug clearance is not limited to renal excretion but encompasses all organs involved in drug elimination,...
Factors Affecting Renal Clearance: Drug Distribution and Drug Interactions
One important factor is the relationship between renal clearance and the apparent volume of distribution. Renal clearance tends to be inversely proportional to the apparent volume of distribution. Drugs with an extensive distribution volume or those...
Hepatic Drug Clearance: Role of Transporters


