Determination of the glomerular filtration rate (GFR) is generally considered as the most important parameter of quantifying renal function. The GFR is determined as renal or plasma clearance of an ideal filtration marker which is freely filtered by the kidney, does not undergo metabolism, tubular secretion or absorption. Markers that fulfil these demands are inulin, 51Cr-EDTA, 99mTc-DTPA, labelled or unlabelled contrast media. The renal clearance of inulin is the classic reference method for estimation of the GFR. This method is however not practical for routine clinical purposes. Radionucleids have therefore been used as alternative filtration markers since the 60s. Drawbacks related to radiation exposure especially in children and pregnant women and the safety in handling radiolabelled markers have led to an increasing interest in using non-radioactive markers. The development of simple and reliable methods to determine the concentration of contrast media in plasma and urine, such as high-performance liquid chromatography (HPLC) and X-ray fluorescence analysis have made this possible. The non-ionic low osmolar contrast medium iohexol has become the most commonly used contrast medium for GFR measurements in Europe. However, other contrast media with similar pharmacokinetics may be equally suitable as GFR markers.

Plasma and renal clearance of iohexol and inulin were similar in healthy adults. Underestimation of GFR was noted when plasma clearance of iohexol and inulin was based on four but not five or more blood samples. Some prediction equations underestimate true GFR to such an extent that caution must be taken when using them to evaluate normal or high GFR values.

The goal of this study was 3-month clinical outcome in nonanticoagulated patients with clinically suspected acute pulmonary embolism (PE) following a negative spiral CT. During a 6-month period 305 patients underwent spiral CT, of whom only 8 also had a lung scintigraphy. In patients with a final CT report read as not positive for acute PE, all hospital records and answers to a patient questionnaire were analyzed for episodes of venous thrombembolism (VTE). Acute PE was diagnosed at spiral CT in 61 patients (20%). Twenty-six of the remaining 244 patients were excluded from further analysis because of (a) long-term anticoagulation due to symptomatic acute deep venous thrombosis (n = 5), clinically diagnosed acute PE (n = 2), chronic recurrent VTE (n = 4), and cardiac disorders (n = 5); and (b) a normal perfusion scintigram (n = 4) or a negative pulmonary arteriogram (n = 6). Three patients were lost to follow-up. Among the remaining 215 patients only 10 had undergone a negative lower extremity venous study. Sixteen patients (7%) died during the follow-up period, 6 of whom underwent autopsy. Venous thrombembolism was diagnosed in three of the 215 patients (1.4%, 95% confidence limits: 0.5-4.0%), one causing the patient's death. Two patients had advanced thoracic malignancies and the third severe chronic obstructive pulmonary disease (84 years old). A negative spiral CT may be able to exclude clinically significant acute PE with the same accuracy as a normal lung scintigraphy or a negative pulmonary arteriography.

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The present study examined the agreement between single and multiple sample plasma clearance of iohexol, a non-ionic contrast agent, in renal failure. Sixty-five patients with varying degree of renal insufficiency received 10 ml iohexol (300 mg I/ml) i.v. and plasma samples were collected four times during the following 3-24 h. Plasma-iodine concentrations were determined by X-ray fluorescence. Predicted creatinine clearance was used to choose one of the samples for determination of single sample clearance. A single plasma specimen collected at 4 h for GFR above 50 ml/min, at 7 h for GFR between 20 and 50 ml/min, and at 24 h for GFR below 20 ml/min gave values in good agreement with those based on a four sample slope clearance. No sign of nephrotoxicity was noted after administration of the contrast agent. It is concluded that single sample plasma clearance after single injection of iohexol gives a good estimate of GFR in renal failure and is advantageous in clinical practice.