Chromium-51 ethylenediamine tetraacetic acid glomerular filtration rate: abetter predictor than glomerular filtration rate calculated by tbe Cockcroft-Gault formula for renal involvement in systemic lupus erythematosus patients

Objective. To investigate whether the ethylenediamine tetraacetic acid (EDT A) glomerular filtration rate (GFR) is a better indicator of the degree of renal involvement than serum creatinine concentration or creatinine clearan ce calculated by the Cockroft- Gault formula. Methods. We studied prospectively all systemic lupus erythematosus (SLE) pa tients with normal or borderline serum creatinine concentration (< 110 <mu> mol/l) and urinary sediment abnormalities and/or proteinuria in the last 2 yr. EDTA-GFR, serum creatinine concentration, calculated creatinine clearan ce (Cockroft-Gault formula) and 24-h urine protein were determined at the s ame time. Renal biopsies were performed in patients with low values of EDTA -GFR or significant proteinuria. Results. Twenty-three patients were identified, of whom 22 were females. Th e average age of the patients was 31.6 +/- 8.2 yr. Biopsies were assigned t o WHO classes as follows: class II, 1 patient; class III, 6 patients; class IV, 10 patients; class V, 6 patients. The average serum creatinine concent ration, EDTA-GFR and calculated creatinine clearance were 79.8 +/- mol/l, 7 4.5 ml/min and 97 ml/min respectively. EDTA-GFR showed abnormal values( < 8 0 ml/min) in 15 of the 23 patients (65.2%) while calculated creatinine clea rance was abnormal ( < 80 ml/min) in three of the 23 patients (13%) (P < 0. 001). Using the Pearson correlation test, we did not find any correlation b etween EDTA-GFR or creatinine clearance values and the sum of activity and chronicity indices. Conclusion. GFR performed by EDTA-GFR correctly predicted renal involvement in SLE patients, whereas GFR calculated by the Cockcroft-Gault formula may have underestimated renal function. Significant numbers of patients with W HO class III, IV or V lupus nephritis may be missed if biochemical creatini ne clearance or serum creatinine concentration alone is used to assess rena l disease.