Trends in persistent proteinuria in adult-onset diabetes: a population-based study.

OBJECTIVE This study investigates temporal trends in the prevalence and incidence of persistent proteinuria among people with adult-onset diabetes (age > or =40 years). RESEARCH DESIGN AND METHODS The complete community-based medical records of all Rochester, Minnesota, residents with a diagnosis of diabetes or diabetes-like condition from 1945 through 1989 were reviewed to determine whether they met National Diabetes Data Group (NDDG) criteria. All confirmed diabetes cases residing in Rochester on 1 January 1970 (n = 446), 1980 (n = 647), and/or 1990 (n = 940) were identified. The medical records of these prevalence cases were reviewed from the time of the first laboratory urinalysis value to the last visit, death, or 1 April 1992 (whichever came first) for evidence of persistent proteinuria (two consecutive urinalyses positive for protein, with no subsequent negative values). Similarly, the medical records of all 1970-1989 diabetes incidence cases (n = 1,252) were reviewed to investigate temporal changes in 1) the likelihood of having persistent proteinuria before the date NDDG criteria was met, i.e., baseline; 2) the risk of persistent proteinuria after baseline; and 3) the relative risk of mortality associated with persistent proteinuria. RESULTS The proportion of diabetes prevalence cases with persistent proteinuria on or before the prevalence date declined from 20% in 1970 to 11% in 1980 and 8% in 1990. Among the 1970-1989 diabetes incidence cases, 77 (6%) had persistent proteinuria on or before baseline; the adjusted odds declined by 50% with each 10-year increase in baseline calendar year (P<0.001). Among individuals free of persistent proteinuria at baseline, 136 subsequently developed persistent proteinuria; the estimated 20-year cumulative incidence was 41% (95% CI 31-59); the adjusted risk did not differ as a function of baseline calendar year. Survival of individuals with persistent proteinuria relative to those without was reduced but did not differ by baseline calendar year. CONCLUSIONS The prevalence of persistent proteinuria among people with adult-onset diabetes in Rochester, Minnesota, declined 60% between 1970 and 1990. The decline appears because of a decrease in the proportion of diabetes incidence cases with persistent proteinuria before baseline rather than secular declines in the risk of persistent proteinuria after baseline or secular increases in the risk of mortality associated with persistent proteinuria. Similarity over time in age and fasting glucose at baseline, and at prevalence dates, is evidence that earlier detection of diabetes is not the sole explanation for the decline.