UNDERSTANDING DIABETES MORTALITY IN AUSTRALIA

WHAT IS DIABETES? Diabetes mellitus is a chronic metabolic condition where glucose levels are too high within the bloodstream. This is due to insulin, a hormone that controls blood glucose levels, no longer being produced or not being produced in sufficient amounts by the body (Diabetes Australia). According to the National Health Survey 2014-15, 5.1% of the Australian population (1.2 million people) had some type of diabetes (excluding persons with gestational diabetes). Type I diabetes affects approximately 0.7% of the population and is an autoimmune disease. Type II diabetes affects around 4.4% of the population and has links to both genetic and lifestyle factors (Diabetes Australia). Currently there is no cure for diabetes, but it can be managed successfully. Despite this, diabetes can lead to many complications which cause or contribute to a person's death. It is referenced on many death certificates, and depending on a range of factors can be assigned either as an underlying or associated cause of death. Understanding mortality associated with diabetes is therefore quite complex and can be examined in a number of different ways. This article presents two different ways of tabulating information on diabetes mortality that both give an insight into the impact of this disease. Information is also provided on diabetes deaths of Aboriginal and Torres Strait Islander people. DIABETES AS AN UNDERLYING CAUSE OF DEATH

The traditional way of tabulating causes of death is by underlying cause. Underlying causes of death are based on the single disease or condition that starts the morbid train of events leading to death. Tabulating causes of death by underlying cause ensures that each death is assigned a single cause and is counted only once in tabulations. However, it does not account for deaths where diabetes was a contributory factor in a person's death. When tabulated as an underlying cause, there were 4,662 deaths due to Diabetes mellitus (E10-E14) in 2015. Diabetes was the sixth leading cause of death, accounting for 2.9% of all deaths. The standardised death rate from diabetes was 16.1 deaths per 100,000 people, and there have been consistently higher rates of death among males compared to females. The death rate has decreased marginally over the past 10 years from 16.6 to 16.1 deaths per 100,000 people. However, it is important to note that the number of deaths has actually increased by close to 1,000 over that same period. Footnote(s): (a) Standardised death rate. Deaths per 100,000 of estimated mid-year population. See Glossary for further information. (b) All causes of death data from 2006 onward are subject to a revisions process - once data for a reference year are 'final', they are no longer revised. Affected data in this table are: 2006-2012 (final), 2013 (revised), 2014-2015 (preliminary). See Explanatory Notes 52-55 and A More Timely Annual Collection: Changes to ABS Processes (Technical Note) in this publication. See also Causes of Death Revisions, 2012 and 2013 (Technical Note) in Causes of Death, Australia, 2014 (cat. no. 3303.0). Source(s): Standardised death rates for Diabetes (E10-E14) in Australia, 2006-2015 (a)(b)-Diabetes SDRs by sex, 2006-2015 For those deaths where diabetes is the underlying cause, it is common for multiple chronic conditions to also appear on the death certificate. In fact, there were an average of 5.1 conditions listed on death certificates where diabetes was the underlying cause, compared with 3.3 conditions listed on all death certificates. Conditions commonly associated with diabetes include heart and kidney diseases. Conditions commonly associated with deaths from diabetes are shown in the graph below. Footnote(s): a) This graph presents deaths for which Diabetes (E10-E14) is the underlying cause of death. The underlying cause of death refers to the disease or injury which initiated the train of morbid events leading directly to death. (b) Associated causes of death are all causes listed on the death certificate other than the underlying cause of death. (c) The associated causes listed are based on the WHO tabulation of leading causes. See Explanatory Notes 34-35 for further information. Groupings of deaths coded to Chapter XVIII: Symptoms, signs and abnormal clinical laboratory findings, not elsewhere classified (R00-R99) are not included in analysis, due to the unspecific nature of these causes. (d) Causes of death data for 2015 are preliminary and subject to a revisions process. See Explanatory Notes 52-55 and A More Timely Annual Collection: Changes to ABS Processes (Technical Note) in this publication. Source(s): Deaths due to diabetes and its leading associated causes, 2015 (a)(b)(c)(d)-Diabetes and its top 5 associated causes

DIABETES-RELATED DEATHS

Diabetes is more likely to be reported as an associated cause of death as opposed to an underlying cause of death. In these instances, the doctor certifying the death recognises that diabetes has contributed to the train of events leading to the person's death, but that it did not initiate that train of events. Many of these deaths could be termed diabetes-related, as a complication of the diabetes, such as heart or kidney disease, is assigned as the underlying cause of death but diabetes is present on the death certificate.

Not all deaths with diabetes as an associated cause are diabetes-related. A definition of those underlying causes that are most likely to signal a diabetes-related death was developed by the United Kingdom Prospective Diabetes Study, and was subsequently modified by the Australian National Diabetes Data Working Group. This definition is provided at the end of the article, and includes all of those deaths for which diabetes is the underlying cause and a selection of other underlying causes for which diabetes is an associated cause.

Using this definition, there were 8,355 diabetes-related deaths in 2015. The standardised death rate for diabetes-related deaths was 28.7 deaths per 100,000 people compared to 16.1 for deaths where diabetes was the underlying cause. Again males have a consistently higher death rate than females, and there has been a marginal decrease in the death rate over time.




DIABETES ON DEATH CERTIFICATES

There is a considerable difference between the number of deaths in a given year with diabetes as the underlying cause (4,662 in 2015), compared with the number of deaths that might be considered diabetes-related (8,355 in 2015). However, there were actually a total of 16,420 deaths in 2015 (10.3% of all deaths) where diabetes was mentioned on a death certificate. Many of these mentions were in Part II of the death certificate. Part II is used by doctors to report other significant diseases, conditions, or injuries that contributed to death but which did not result in the underlying cause of death given in Part I. The use of Part II for recording diabetes mostly precludes it from being chosen as the underlying cause of death, but the fact it is mentioned is significant and is likely to be of interest to researchers and policy makers working on related matters.


DIABETES IN THE ABORIGINAL AND TORRES STRAIT ISLANDER POPULATION

Aboriginal and Torres Strait Islander deaths include those recorded in New South Wales, Queensland, Western Australia, South Australia and the Northern Territory. Data for Victoria, Tasmania and the Australian Capital Territory have been excluded in line with national reporting guidelines (for information on issues with Aboriginal and Torres Strait Islander identification, see Explanatory Notes 56-66).

Diabetes (E10-E14) was the second leading underlying cause of death of Aboriginal and Torres Strait Islander Australians in 2015, accounting for 194 deaths, or 6.7% of all Aboriginal and Torres Strait Islander deaths. The standardised death rate for diabetes was 4.7 times higher for Aboriginal and Torres Strait Islander Australians compared to non-Indigenous Australians in 2015 (76.9 and 16.3 deaths per 100,000 people, respectively). However, the rate is also the lowest recorded for Aboriginal and Torres Strait Islander people in the past 5 years.




DEFINITION OF DIABETES-RELATED DEATHS

2.3 DIABETES-RELATED DEATHS, Specified ICD-10 codes(a)(b)
Diabetes-Related Deaths		ICD-10 Codes
Diabetes is listed as the underlying cause of death		E10, E11, E13, E14, O24
Diabetes is listed as an associated cause of death, where the underlying cause of death was one of:
	Myocardial infarction (heart attack)	I21-I22
	Ischaemic heart disease	I20, I24-I25
	Stroke or sequelae of stroke	I60-I64, I69.0-I69.4
	Heart failure	I50
	Sudden death (cardiac arrest)	I46
	Peripheral vascular disease	I70-I74
	Kidney disease	N00-N28
	Hyperglycaemia	R73
	Hypoglycaemia	E16.1-E16.2
(a) Source National indicators for monitoring diabetes, AIHW 2007 (b) ‘Diabetes-related deaths’ is based on the definition of ‘deaths related to diabetes’ used in the United Kingdom Prospective Diabetes Study (UKPDS 1998). The UKPDS definition has been modified by diabetes specialists on the National Diabetes Data Working Group (NDDWG) to include ischaemic heart disease, sequelae of stroke and heart failure, and other commonly recognised complications of diabetes.