MONITORING KIDNEY-FUNCTION IN DIABETIC NEPHROPATHY

Progression in diabetic nephropathy is usually determined by repeated measurements of glomerular filtration rate and expressed as rate of de cline in glomerular filtration rate. Our aim was to evaluate the agree ment between rate of decline in glomerular filtration rate estimated f rom the Cockroft-Gault formula: (140-age)K*body weight*(1/S-creatinin e) and measured by the plasma clearance of Cr-51-EDTA. All insulin-dep endent diabetic patients with diabetic nephropathy followed-up for at least 5 years with at least 5 simultaneous measurements of glomerular filtration rate, s-creatinine, and weight were included in the study. Forty-three patients (32 male/11 female), age 31 (18-61) years were en rolled. Observation period: 6.6 (5.1-9.9) years and number of investig ations per patient 6 (5-16) (median(range)). Baseline glomerular filtr ation rate (ml/min) was 97 (30) measured and 107 (37) estimated (mean( SD))(p < 0.001) and the 95% limits of agreement were -42.0 to 20.8 ml/ min. Measured and estimated glomerular filtration rate correlated sign ificantly (r = 0.91, p < 0.00 001). Rate of decline in kidney function ml . min(-1) . year(-1) was 4.7 (3.3) measured and 4.8 (3.5) estimate d (mean(SD)) (NS), but the 95% limits of agreement showed a wide range -3.9 to 3.5 ml . min(-1) . year(-1). A significant correlation betwee n rate of decline in measured and estimated glomerular filtration rate was present (r = 0.84, p < 0.00 001). In conclusion, glomerular filtr ation rate is overestimated by the Cockroft-Gault formula. The mean ra tes of decline in glomerular filtration rate are comparable, but the l imits of agreement are wide, which make the Cockroft-Gault method unac ceptable for clinical purposes, i.e. monitoring progression in kidney function in the individual patient. However, the estimated glomerular filtration rate may be used for comparison of groups in observational studies and in clinical trials with a long observation period.