Plasma clearance of iodine contrast media as a measure of glomerular filtration rate in critically ill patients

Objective. The selection of the optimal method for assessing renal function relies on the accuracy of the technique. Plasma clearance of nonradioactiv e iodine contrast media (i.e., iohexol or iopromide) has been suggested as a reliable alternative to the renal clearance of inulin for estimating glom erular filtration rate (GFR). The accuracy of this method when used with cr itically ill patients displaying different levels of renal function in an i ntensive care unit (ICU) has not, until now, been examined. Design. The accuracy of double-and multiple-point iohexol or iopromide plas ma clearances was compared with that of already established techniques for measuring GFR (creatinine clearance, formula clearance by Cockcroft and Gau lt) and with that of inulin clearance, which is regarded as the gold standa rd for the measurement of GFR. Patients. Values were obtained from 31 ICU patients who exhibited a wide ra nge of renal function (serum creatinine: 0.6-6.7 mg/dL). Measurements. Inulin clearance was performed using the constant-infusion te chnique. Creatinine clearance was determined from 24-hr urine samples. The clearance formula was calculated according to Cockcroft and Gault's formula . Iohexol or iopromide were applied as a single intravenous dose, and blood samples were taken up to 6 hrs after the injection. Iodine concentrations were determined by radiographic fluorescence. Results. Plasma clearance of iohexol/iopromide measured after the single in jection of contrast media and that of the conventional inulin clearance was almost identical (y = 0.971x + 7.65, r(2) = .96; n = 31). Two-point cleara nce of iohexol/iopromide (double sampling technique) was as reliable as the three-point clearance (three-slope-intercept method, y = 0.995x + 0.62, r( 2) = .999; n = 18). With respect to inulin clearance, GFR measurements dete rmined by creatinine clearance or according to the formula given by Cockcro ft and Gault revealed errors that increased proportionally (y = 1.03x, r(2) =.88; n = 27; and y = 0.93x, r(2) = .62; n = 31, respectively). It could a lso be shown that the accuracy of GFR measurements involving plasma clearan ce of iohexol was not greatly affected by the degree of renal insufficiency or the route by which contrast media were applied. Conclusion. These findings indicate that the determination of plasma cleara nce of iohexol/iopromide is a simple, rapid, and accurate method that can i ndeed be used for estimating GFR in ICU patients with normal renal function or even different degrees of renal insufficiency.