Mortality trends in type 1 diabetes. The Allegheny County (Pennsylvania) Registry 1965-1999

Abstract

Objectives: To investigate long-term mortality and its temporal trends as of 1 January 1999 among the 1,075 patients with type 1 diabetes (onset age <18 years, diagnosed between 1965 and 1979) who comprise the Allegheny County population-based registry.

Research design and methods: Overall, sex- and race-specific mortality rates per person-year of follow-up were determined. Standardized mortality ratios were also calculated. Survival analyses and Cox proportional hazard model were also used. Temporal trends were examined by dividing the cohort into three groups by year of diagnosis (1965-1969, 1970-1974, and 1975-1979).

Results: Living status of 972 cases was ascertained as of January 1, 1999 (ascertainment rate 90.4%). The mean duration of diabetes was 25.2 +/- 5.8 (SD) years. Overall, 170 deaths were observed. The crude mortality rate was 627 per 100,000 person-years (95% CI 532-728) and standardized mortality ratio was 519 (440-602). Life-table analyses by the Kaplan-Meier method indicated cumulative survival rates of 98.0% at 10 years, 92.1% at 20 years, and 79.6% at 30 years duration of diabetes. There was a significant improvement in the survival rate between the cohort diagnosed during 1965-1969 and that diagnosed during 1975-1979 by the log-rank test (P = 0.03). Mortality was higher in African-Americans than in Caucasians, but there were no differences seen by sex. The improvement in recent years was seen in both ethnic groups and sexes.

Conclusions: An improvement in long-term survival was observed in the more recently diagnosed cohort. This improvement is consistent with the introduction of HbA1 testing, home blood glucose monitoring, and improved blood pressure therapy in the 1980s.