INSULIN-TREATED DIABETES-MELLITUS - CAUSES OF DEATH DETERMINED FROM RECORD LINKAGE OF POPULATION-BASED REGISTERS IN LEICESTERSHIRE, UK

Study objective - Analyses of causes of mortality in people with diabe tes using data from death certificates mentioning diabetes provide unr eliable estimates of mortality. Under-recording of diabetes as a cause on death certificates has been widely reported, ranging from 15-60%. Using a population based register of people with diabetes and linking data from this with causes of death data from another source is a viab le alternative. Data from the Office of Population Censuses and Survey s (OPCS) are the most acceptable mortality data available for such an exercise, as direct comparison with other published mortality rates is then possible. Design - A locally maintained population-based mortali ty register and all insulin-treated diabetes mellitus cases notified t o the Leicestershire diabetes register (n = 4680) were linked using re cord linkage software developed in-house (Lynx). This software has bee n extensively used in a maintenance and update cycle designed to maxim ise accuracy and minimise duplication and false registration on the di abetes register. Deaths identified were initially coded locally to the International Classification of Diseases, 9th revision (ICD9), and la ter a Linkage was performed to use official OPCS coding. Mortality dat a identified by the Linkage was indirectly standardised using populati on data for Leicestershire for 1991. Standardised mortality ratios (SM R) were estimated, with 95% confidence intervals. Insulin dependent di abetes (IDDM) was defined as diabetes diagnosed before age 30 years wi th insulin therapy begun within one year of diagnosis. All other types were considered non-insulin dependent diabetes (NIDDM). Analyses were performed for the whole sample and then for the NIDDM subgroup. Resul ts from these analyses were similar and therefore only whole group ana lyses are presented. Main results - A total of 370 deaths were identif ied for the period 1990-92 inclusive - 56% were in men and 44% in wome n, median age (range) 71 years (12-94). Approximately 90% of deaths we re subjects with NIDDM. Diabetes was mentioned on 215 (58%) death cert ificates. The all causes SMRs were significantly raised for men and wo men for all ages less than 75 years. Ischaemic heart disease (ICD9 rub rics 410-414) accounted for 146 (40%) deaths 41% of male and 38% of fe male deaths. Male and female SMRs were significantly raised for the ag e groups 45-64, 65-74, and 75-84 years. Cerebrovascular disease (ICD9 rubrics 430-438) accounted for 38 (10%) deaths and the SMR for women w as significantly raised. For women the external causes of death (ICD9 rubrics E800-E999) were also significantly raised overall and in age g roups 15-44 and 45-64 years. This was not true for men, although numbe rs of deaths in this category were small for both men (4) and women (9 ). Conclusions - Record linkage has been used successfully to link two local, population based registers. This has enabled an analysis of mo rtality in people with diabetes to be performed which overcomes the pr oblems associated with using as a sample, death certificates where dia betes is mentioned. The mortality rates and SMRs estimated should more accurately reflect the true rates than would be possible using other methods. The persisting excess mortality identified for people with di abetes is of a similar magnitude and attributable to similar causes as has been reported elsewhere in population based studies.