Prevalence of diagnosed and undiagnosed Type 2 diabetes in a Queensland Aboriginal community

Hilary Bambrick
School of Archaeology & Anthropology
The Australian National University

Suggested citation: Bambrick H (2001, 1 August) Prevalence of diagnosed and undiagnosed Type 2 diabetes in a Queensland Aboriginal community. Australian Indigenous HealthBulletin, 1(1), Article 1. Retrieved [access date] from http://www.healthinfonet.ecu.edu.au/html/html_bulletin/bull_11/bulletin_original_articles.htm

Introduction

Life-expectancy for Indigenous people is about 20 years less than for the rest of Australia [1], and more than half of all Indigenous men die before they reach the age of 50 years [2]. Type 2 diabetes is both a major contributor to and a direct cause of excess morbidity and mortality. It is frequently linked to socioeconomic status, with lifestyle identified as the primary proximal cause. Arising from experiences of dispossession and continuing marginalisation, many Indigenous people share similar social and economic circumstances that place them at increased risk of Type 2 diabetes.

Estimates of the overall prevalence of diabetes among Indigenous groups range between 10 and 30%, or two to four times the prevalence for non-Indigenous people [3]. For Australia as a whole, it has been suggested that there is one undiagnosed diabetic for every person who has been diagnosed [4].

The research reported here was carried out in a large Aboriginal community in south-east Queensland between September and December 2000. It is standard practice at the community hospital that random blood glucose is measured whenever a person presents for treatment if they hadn’t been tested in the previous three months. The hospital serves the entire community, so there is significant opportunity for early diagnosis and treatment. It was not known, however, whether this had reduced the proportion of undiagnosed diabetics within the community.

Methods

Diagnosed diabetes prevalence

In the absence of a general medical practice, the community hospital functions as an outpatient clinic. Details of all patient visits, diagnoses and treatments are kept on a computerised database. The database includes people whose diabetes had been diagnosed or confirmed after 1996. To calculate age-specific prevalences, records of current patients with diagnosed diabetes who were resident in the community were used in conjunction with population figures from the 1996 Census of Population and Housing.

Undiagnosed diabetes prevalence

People who had never been diagnosed with diabetes were selected through random household sampling, where one adult from each house was asked to participate. Out of eligible households (several households contained only adults diagnosed with diabetes), there was an overall response rate of 55%. If only houses where contact was made are included, the response rate was 69%.

Fasting blood sugar level (BSL), blood pressure, body mass index (BMI) and waist circumference were measured for cases and people who had never been diagnosed with diabetes. Among the people who had never been diagnosed, diabetes was considered to be ‘unlikely’ if fasting BSL was below 5.5mmol, and ‘likely’ if it were 7.0mmol or greater [5]. Those with impaired fasting glucose (IFG), where BSL fell between 5.6 and 6.9 inclusive, were classified as ‘uncertain’.

Recent evidence-based draft guidelines [5] suggest that the presence of three or more independent risk factors together confers significantly higher risk of diabetes than two or fewer, with risk doubling for each of the following:

All those who returned fasting BSLs in the ‘likely’ category were re-categorised as cases, as were people who had never been diagnosed with diabetes but who had IFG and who exhibited three or more of the five risk factors. Including those for whom development of the disease seems imminent with the less ambiguous ‘likely’ group should reflect more accurately the reality of the diabetes burden within the community.

Results

Diagnosed diabetes prevalence

The overall prevalence of diagnosed diabetes among adults within this community was about 20% for both females and males (Table 1). Prevalence increases sharply with age, with two-thirds of females and nearly half of males over 40 years having diagnosed diabetes.

Table 1. Prevalence of diagnosed Type 2 diabetes, south-east Queensland Aboriginal community, 2000  

Note: Prevalence for ‘all ages’ is the crude prevalence

Undiagnosed diabetes prevalence

Random sampling provided 105 people who had never been diagnosed with diabetes (58 females 44 males), nearly a quarter of the non-diagnosed adult population. Women were more likely to take part than men (25% compared with 20% of the non-diagnosed population).

Using fasting BSL, three (5.2%) female who had never been diagnosed with diabetes were ‘likely’ to have diabetes, as were six males (13.6%). IFG was found in 31% of women and 43% of men. Of these, 61% of women and 32% of men exhibited three or more other independent risk factors for diabetes.

In total, 24% (14 out of 58 participants, mean age 34.1 years, range 28 to 46) of women and 27% (12 of 44, mean age 34.1 years, range 27 to 41) of men who had never been diagnosed with diabetes either had undiagnosed diabetes or were at very high risk of developing it, and were re-classified as undiagnosed ‘cases’.

The ratios of undiagnosed diabetics to diagnosed diabetics in this community were thus determined (for females and males separately):

undiagnosed (%) * (total adult population n – diagnosed n)
diagnosed n

For every diagnosed woman, there were 0.9 women with undiagnosed diabetes (or who are very likely to develop it) and 1.1 undiagnosed men for every diagnosed man.

Using the formula:

diagnosed n + estimated undiagnosed n
adult population n

the probable overall prevalence was estimated at 40% for females and 42% for males.

Discussion

The prevalence of diagnosed diabetes within this community is very high compared with the national level. The inclusion of likely undiagnosed cases (based on fasting BSL of 7.0mmol or greater or the presence of IFG plus three or more other independent risk factors for diabetes), results in an estimated overall prevalence of around 40%.

Despite routine hospital screening for diabetes, the ratios of undiagnosed to diagnosed diabetes were very similar to those for Australian overall. In some age groups, however (such as women over 50 years), more than half had already been diagnosed. Higher proportions of undiagnosed diabetes occurred in the younger groups: the mean ages of undiagnosed women and men were only 34 years.

A slightly greater proportion of males than females was likely to have been undiagnosed. There are several possible reasons for this. Men in general in Australia are less likely than women to visit their doctor or seek health other advice, and this is especially true of Indigenous men, men in rural areas and those from other marginalised groups [2]. This may be reflected also in the lower participation by men than women in this study. Women may have been more likely to participate because they take greater interest in their health generally, seeing themselves more as active agents than passive recipients when it comes to health care. Diabetes may also be diagnosed more frequently in women due to screening for gestational diabetes.

Risk-taking behaviour is also more likely among men than women, especially young men, and particularly those who are disaffected and feel that there is little to lose [6]. This may manifest in behaviours that are more likely to lead to undiagnosed diabetes, such as frequent or heavy drinking of alcohol, poor diet, physical inactivity, and fewer health checks. Being both male and socially disadvantaged combine to produce the worst outcomes for health [7].

The high level of undiagnosed diabetes overall, despite hospital screening, may be due in part to inadequate follow-up of patients who requires further testing with an oral glucose tolerance test (OGTT) necessary for diagnosis. In several cases of diagnosed diabetes, there had been considerable delays (of two to nine years) between a questionable random glucose result and the request for an OGTT.

Random BSLs are measured at most visits to the hospital, regardless of the complaint. As most people make use of the hospital as their only point of health care, there is a considerable opportunity for diabetes to be picked up through incidental testing. The community as a whole is also aware that diabetes is a major health problem. It is uncertain what the prevalence of undiagnosed diabetes would be if the hospital did not conduct routine screening. Without routine screening, the level of undiagnosed diabetes in this community may have been even higher. It is clear, however, that the outcomes of these routine tests could be used more wisely, and that screening is relatively worthless unless there is adequate follow-up of those at risk.

IFG may represent a stage in the development of the disease. The high level of IFG in this population may indicate that it is on the brink of a major epidemic of Type 2 diabetes and its associated health problems. It provides further evidence for the need for more rigorous post-screening follow-up in this at-risk population.

Acknowledgements

The author would like to thank the Aboriginal community involved for their warm welcome and interest in this study, in particular the participants and the members of the Community Health Team. Many thanks go to the Australian Institute of Aboriginal and Torres Strait Islander Studies for financial assistance (AIATSIS grant number S6116076), and to Antonia Kirk and Maureen Weazel for their invaluable help.

References

1. Cunningham J, Paradies Y (2000) Mortality of Aboriginal and Torres Strait Islander Australians, 1997. Canberra: Australian Bureau of Statistics Occasional paper.

2. Australian Institute of Health and Welfare (2000) Australia’s health 2000. The seventh biennial health report of the Australian Institute of Health and Welfare. Canberra: Australian Institute of Health and Welfare.

3. de Courten M, Hodge A, Dowse G, King I, Vickery J, Zimmet P (1998) Review of the epidemiology, aetiology, pathogenesis and preventability of diabetes in Aboriginal and Torres Strait Islander populations. Canberra: Commonwealth Department of Health and Family Services.

4. Commonwealth Department of Health and Aged Care and Australian Institute of Health and Welfare (1999) National Health Priority Areas Report – diabetes mellitus 1998. Canberra: Commonwealth Department of Health and Aged Care and Australian Institute of Health and Welfare.

5. Australian Centre for Diabetes Strategies (2000) National evidence-based guidelines for the management of type 2 diabetes mellitus: public consultation draft prepared for the Diabetes Australia Guideline Development Consortium. Sydney: Australian Centre for Diabetes Strategies, Prince of Wales Hospital.

6. Chisholm J (1996) The young male syndrome: the evolutionary psychology of risk-taking in young men. In: Robinson G, ed. Aboriginal health: social and cultural transitions: Proceedings of a conference at the Northern Territory University, Darwin, 29-31 September 1995. Darwin: Centre for Social Research and the Faculty of Aboriginal and Torres Strait Islander Studies, NTU.

7. Connell RW, Schofield, T, Walker, L, Wood, J, et al. (1998) Men’s health: a research agenda and background report. Canberra: Commonwealth Department of Health and Aged Care.