THE UNCHANGING INCIDENCE OF HOSPITALIZATION FOR DIABETIC NEPHROPATHY IN A POPULATION-BASED COHORT OF IDDM PATIENTS IN FINLAND

OBJECTIVE -- Finland has the highest documented incidence of childhood IDDM in the world, but the incidence of diabetic nephropathy in Finla nd is unknown. The aim of the present study was to determine the incid ence of hospitalization for diabetic nephropathy in a population-based cohort of Finnish IDDM patients and to analyze the prognostic effect of sex, age at diagnosis, and calendar year of diagnosis of IDDM. RESE ARCH DESIGN AND METHODS -- We included all Finnish patients who had on set of IDDM before age 18 years, were diagnosed between January 1965 a nd December 1979 (n = 5,149), and were traced for hospitalizations bet ween January 1970 and the end of December 1989 in the Hospital Dischar ge Register, using the unique personal identification code given to al l Finnish citizens. The development of diabetic nephropathy was define d as the first hospitalization with a diagnosis of nephropathy (Intern ational Classification of Diseases-8th Revision [ICD-8] 250.04, or 9th Revision [ICD-9] 2503B/2503X). RESULTS -- Among the 5,149 patients in cluded, we identified 446 cases of diabetic nephropathy. The incidence of hospitalization for diabetic nephropathy was very low during the f irst 8 years of diabetes duration, and after that increased to a maxim um of 1.6-2.0% per year. Female subjects developed nephropathy slightl y earlier than male subjects, but the cumulative risk was independent of sex. Patients diagnosed at ages 5-14 years had the highest risk of hospitalization for diabetic nephropathy. We observed no effect of cal endar year of diagnosis. CONCLUSIONS -- We found a 2046 cumulative inc idence of hospitalization for diabetic nephropathy during a total 24 y ears of IDDM duration. This finding is compatible with the cumulative incidence of hospitalization for diabetic nephropathy found in other E uropean populations. The incidence of hospitalization for diabetic nep hropathy did not decrease during the 20-year observation period.