Aims: To estimate the degree of under-reporting of diabetes on death certificates, and to describe the population of patients enrolled on the Otago Diabetes Register known to have died during the 6-year period to 31 December 2003.
Methods: The Otago Diabetes Register was established in 1998, as part of the Otago Diabetes Project, to monitor and evaluate diabetes care in the Otago region, New Zealand. Demographic and clinical data, including vital status, type of diabetes and year of diagnosis, diabetes complications, diabetes medication and clinical examination, and biochemistry test results were collected annually from general practice medical records. Copies of death certificate information were obtained from the national Births, Deaths and Marriages office, Department of Internal Affairs for 508 enrolled diabetic patients known to have died before 31 December 2003. Causes of death were coded using ICD-10. Date, place, and causes of death were added to the Otago Diabetes Register.
Results: The mean age at death was 78 years (SD=9.7) and the average duration of diagnosed diabetes was 12.1 (SD=8.6) years. Diabetes was mentioned on the death certificates of just over half (55.1%) of the 508 diabetic patients. More of those using insulin only, or oral hypoglycaemic and insulin therapies combined, before death had diabetes mentioned on their death certificate, 67.8% and 81.0%, respectively, compared with those taking oral hypoglycaemics only (55.7%) or diet only treatment (38.0%). Almost 50% of deaths were due to a circulatory system disorder, either cardiovascular or cerebrovascular disease. Five men with type 1 diabetes, all aged less than 50 years, died from diabetic ketoacidosis or hypoglycaemia.
Conclusion: Diabetes is under-reported on death certificates in New Zealand. Improvements in the completion of death certificates are necessary, if the impact of the diabetes epidemic on mortality is to be monitored appropriately.