ONTRAST NEPHROPATHY IS A recognized complication after coronary angiography and intervention that has been associated with prolonged hospitalization and adverse clinical outcomes. 1-3 It is reported that 14.5% of patients develop a 25% increase in serum creatinine levels following cardiac catheterization. 2 This problem assumes greater and greater importance with increased use of invasive radiological procedures to diagnose and treat coronary artery disease. Contrast nephropathy is potentially preventable because the administration of radiocontrast agent is predictable and high-risk populations also have been identified. 4 Patients at greatest risk are those with impaired renal function, 5 particularly that caused by diabetic nephropathy. 6 However, other than the use of intravenous hydration 2 and lowosmolality contrast media, 7 no previ-Author Affiliations:

The patients were participants in a study of renal function in those aged over 40 years, of whom there were 158 on the clinic register. From these, 38 patients (17 men, 21 women) were selected on the basis of serum creatinine concentrations, to provide a range of predicted glomerular filtration rates, and 21 of these (eight men, 13 women) had detailed studies performed including creatinine clearance. The mean age of all subjects was 50 7 years (range 41 6-73-5 years). All were in the steady state and gave informed consent to the study.Creatinine clearance was based on a timed and closely supervised five hour urine collection, each patient being given 400 ml water orally before the test and unlimited fluid on demand during the test. Serum and urine samples were frozen to -70°C for transport to Oxford where creatinine clearance was estimated by the alkaline picrate reaction (Department of Clinical Biochemistry, John Radcliffe Hospital, Oxford). 5'Cr-EDTA clearances were performed concurrently with creatinine clearance using the single injection method" and 5'Cr-EDTA from Amersham Radionucleotides (Amersham UK). Serum radioactivity was counted in a multichannel spectrum analyser calibrated to the peak emission of 5'Cr (Centre for Nuclear Sciences, University of the West Indies). Samples for serum f2 microglobulin were taken at the midpoint of the five hour urine collection period, frozen immediately, and transported to Oxford for estimation by radioimmunoassay (Pharmacia Diagnostics; Department of Nuclear Medicine, Radcliffe Infirmary, Oxford). ResultsEstimates of serum #2 microglobulin and of 5'Cr-EDTA clearance were performed in all 38 subjects whereas creatinine clearance and serum creatinine were measured in a subset of 21 patients (table). Creatinine clearance was linearly associated with 5'Cr-EDTA clearance (r = 0 84, p < 0 01) (fig 1), although creatinine clearance seems to underestimate proportionally GFR. On average, creatinine clearance values were 24 4 ml/minute (32%0) below those obtained by the isotope method, the difference between paired values being highly significant (Student's t test = 4 51, p < 0-0002). The 370 on 7 May 2018 by guest. Protected by copyright.

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