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 Finland is unknown. The aim of the present study was to determine the incidence 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. RESEARCH DESIGN AND METHODS We included all Finnish patients who had onset of IDDM before age 18 years, were diagnosed between January 1965 and December 1979 ( n = 5,149), and were traced for hospitalizations between January 1970 and the end of December 1989 in the Hospital Discharge Register, using the unique personal identification code given to all Finnish citizens. The development of diabetic nephropathy was defined as the first hospitalization with a diagnosis of nephropathy ( International Classification of Diseases-8th Revision [ICD-8] 250.04, or 9 th Revision [ICD-9] 2503B/2503X). RESULTS Among the 5,149 patients included, we identified 446 cases of diabetic nephropathy. The incidence of hospitalization for diabetic nephropathy was very low during the first 8 years of diabetes duration, and after that increased to a maximum of 1.6–2.0% per year. Female subjects developed nephropathy slightly 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 calendar year of diagnosis. CONCLUSIONS We found a 20% cumulative incidence of hospitalization for diabetic nephropathy during a total 24 years of IDDM duration. This finding is compatible with the cumulative incidence of hospitalization for diabetic nephropathy found in other European populations. The incidence of hospitalization for diabetic nephropathy did not decrease during the 20-year observation period.