The plasma clearance of iohexol has recently been proposed as a new method for estimating GFR. The iohexol plasma clearance was compared with that of ⁵¹Cr-EDTA in 32 diabetic patients (12 IDDM, 20 NIDDM; age 23–70; diabetes duration 1–35 years) with normal to impaired renal function (serum creatinine: 0.8–6.4 mg/dL). Bolus i.v. injection of ⁵¹Cr -EDTA (1 μCi/kg) was followed by 5 mL slow i.v. injection of Omnipaque (Nycomed Oslo, Norway). Samples for radioactivity and iohexol analysis were drawn at 0, 5, 10, 15, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300 min (+360 and 420 min if serum creatinine > 2.0; + 1440 min if > 5.0 mg/dL). Iohexol was assayed in duplicate by HPLC throughout a Nova-Pak C18 column (Waters-Millipore, USA). Only the second peak obtained during elution of iohexol (about 4.5 min) was used for calculation. Dilution tests show highly linear regressions for concentrations between 3.25–650 μg/mL (r=0.99). Imprecision of iohexol assay (the whole procedure from deproteinization to chromatography) was: infra-assay 1.4 ± 1.5%, mlsd (95% CI: 1.0–1.8%); inter-assay 3.0 ± 2.7% (1.4–4.6%). Iohexol plasma clearance ranged between 12.9 and 150.9 mL/min, while ⁵¹Cr -EDTA plasma clearance between 11.9 and 149.8 mL/min with excellent correlation (iohexol = 0.98 ⁵¹Cr -EDTA +2.49; r = 0.995). Mean CV between the two methods was 1.7% (range 0–4.9%) with a significant negative correlation (r = 0.5 1p = 0.007) with the GFR levels. Correlation between repeated measurements, performed in eight patients, was excellent (r =−0.994, p = 0.0001).

In diabetics, GFR measured by plasma clearance of iohexol shows an excellent agreement with plasma clearance of ⁵¹Cr r-EDTA throughout a wide range of renal function. iohexol provides an accurate alternative method for measuring GFR.