Recommendations: Type 2 diabetes prevention and early detection
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Preventive intervention type
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Who is at risk?
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What should be done?
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How often?
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Level/ strength of evidence
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References
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Screening
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Adults aged ≥18 years, particularly adults with any of the following high-risk conditions:
- previous impaired glucose tolerance (IGT) or impaired fasting glucose (IFG) (Box 2)
- history of gestational diabetes mellitus
- history of polycystic ovary syndrome
- history of cardiovascular disease
- current antipsychotic medication use
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Measure fasting plasma glucose or random venous blood glucose or HbA1c
A laboratory test is preferable, but finger prick (point-of-care) testing is an alternative
Perform oral glucose tolerance test (OGTT) in those with equivocal results
The 2012 World Health Organization or International Diabetes Federation criteria46 should be used to diagnose type 2 diabetes
(Box 1)
Given the high prevalence of diabetes, use of screening tools such as AUSDRISK is likely to be of limited benefit |
Annually as part of adult health check |
IIB
GPP |
1 |
People aged <18 years with overweight or obesity |
Consider the potential for early onset type 2 diabetes and consider testing according to clinical context (refer also to Chapter 1: Lifestyle, ‘Overweight and obesity’) |
Opportunistic |
GPP |
41 |
Behavioural
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All people
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Measure body mass index (BMI) and waist circumference (refer to Chapter 1: Lifestyle: ‘Overweight and obesity’)
Advise minimum of 30 minutes moderate activity on most days (refer to Chapter 1: Lifestyle, ‘Physical activity’)
Encourage diet rich in vegetables, fruits, legumes, high-fibre cereals, fish and lean meats. Limit fats, salt, sugar and alcohol (refer to Chapter 1: Lifestyle, ‘Overweight and obesity’)
For people overweight or obese, refer to Chapter 1: Lifestyle, ‘Overweight and obesity’ |
Opportunistic and as part of annual health assessment |
IA |
1, 26 |
People with BMI ≥35 kg/m2 |
Advise intensive lifestyle modification as above
Discuss risks and benefits of bariatric surgery and consider referral if services are available (refer to Chapter 1: Lifestyle, ‘Overweight and obesity’) |
Opportunistic |
IIIC |
1 |
Chemo-prophylaxis
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People with a high-risk condition (refer above)
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Advise intensive lifestyle modification as above
If lifestyle modification is unable to be achieved, the use of metformin, acarbose, or orlistat has been shown to delay or prevent the onset of diabetes. However, these medications all have potential risks. None are Pharmaceutical Benefits Scheme (PBS) funded for people without diagnosed diabetes, and their use is not recommended |
Opportunistic |
IB |
1 |
Environmental
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Communities |
Advocate for multifactorial and coordinated communitybased interventions to increase access to healthy and nutritious food and promotion of increased physical activity (refer to Chapter 1: Lifestyle: ‘Overweight and obesity’ and ‘Physical activity’) |
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GPP |
42–45 |
Box 1. Diagnostic definitions of type 2 diabetes46
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Diabetes can be diagnosed on any of the following criteria:
- Fasting plasma glucose (FPG) ≥7.0 mmol/L
- 75 g oral glucose tolerance test (OGTT) with FPG ≥7.0 mmol/L and/or two-hour plasma glucose ≥11.1 mmol/L
- Glycated haemoglobin (HbA1c) ≥6.5%/48 mmol/mol
- Random plasma glucose ≥ 11.1 mmol/L in the presence of classical diabetes symptoms
Asymptomatic individuals with a single abnormal test should have the test repeated to confirm the diagnosis unless the result is unequivocally elevated.
Where a random plasma glucose level ≥5.6 mmol/L and <11.1 mmol/L is detected, an FPG should be measured, an OGTT performed, or an HbA1c measured.
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Box 2. Prediabetes: Diagnostic definitions of impaired fasting glucose (IFG) and impaired glucose tolerance (IGT)11
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The presence of prediabetes is defined according to the results of a two-hour oral glucose tolerance test (OGTT).
IFG:
- fasting glucose 6.1–6.9 mmol/L, and
- two-hour glucose <7.8 mmol/L
IGT:
- fasting glucose <7 mmol/L, and
- two-hour glucose ≥7.8 mmol/L and ≤11 mmol/L.
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Background
Type 2 diabetes is a progressive condition in which the body loses the capacity to produce enough insulin and/or becomes resistant to insulin’s effects. This usually develops slowly over years, providing a substantial ‘pre-diabetic’ window period of opportunity to offer preventive interventions. Screening for diabetes is safe, accurate and cost effective, and detects a substantial proportion of people who may not otherwise have received early intervention.1 This guide discusses the prevention of type 2 diabetes in adults who are not pregnant. It does not address how to manage type 2 diabetes, for which readers are encouraged to consult clinical guidelines.2
One in nine Aboriginal and Torres Strait Islander adults has diabetes,3 with the prevalence of type 2 diabetes being 3.3 times higher at any age than for the general Australian population, and type 2 diabetes is a direct or indirect cause for 20% of Aboriginal and Torres Strait Islander people’s deaths.4 Diabetes prevalence in remote populations (21%) is more than double that of non-remote populations (9%)4 and is higher among Torres Strait Islander peoples than Aboriginal peoples.5
Large clinical trials have demonstrated that appropriate management of diabetes can prevent the development or delay the progression of complications such as myocardial infarction, eye disease and renal failure.6 Obesity is a very strong predictor for diabetes; Aboriginal and Torres Strait Islander adults who are obese are seven times as likely as those of normal weight or underweight to have diabetes (17% compared with 2.4%).4 A cohort study of non-diabetic Aboriginal adults aged 15–77 years in Central Australia found that those with a body mass index (BMI) of ≥25 kg/m2 had 3.3 times the risk of developing diabetes over eight years of follow-up compared to those with BMI of <25 kg/m2.1 The AusDiab study found that three measures of obesity – BMI, waist circumference and waist-to-hip ratio – all had similar correlations with diabetes and CVD risk.7
Interventions
Screening
Type 2 diabetes can be a disease with few or no symptoms, so is prone to under-diagnosis. A small 2008 study of Aboriginal and Torres Strait Islander people in Darwin found an overall diabetes prevalence of 17%, of which one-third were previously undiagnosed. When those undiagnosed were assessed for diabetes complications, 19% had albuminuria, 14% had peripheral vascular disease, 6% had neuropathy and none had retinopathy.8
Screening for undetected diabetes is an efficient method of preventing complications from this disease.1 Screening for diabetes will also detect prediabetes – impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG). The biochemical criteria for diabetes are listed in Box 1, and those for IGT and IFG are listed in Box 2. Prediabetes is not a disease, and there is some controversy as to the benefits of diagnosing it,9 because risk reduction should ideally be promoted regardless of giving the condition a label. Prediabetes is a marker for higher risk of developing diabetes and cardiovascular disease (CVD), although diagnosing prediabetes via screening has been shown to be inaccurate.10
Screening for diabetes in non-pregnant adults should be done on an opportunistic basis in the primary care setting, rather than in mass screening programs (evidence level IV).1 Aboriginal and Torres Strait Islander people should be screened for diabetes from age 18 years, rather than from 40 years as in the general Australian population.1
The recommended screening method for the general population is using AUSDRISK,11 a risk assessment tool that asks questions about age, gender, ethnicity, family history, hypertension, smoking, diet, physical activity and obesity. AUSDRISK is available online or as a printout,12 and those scoring ≥12 proceed to biochemical blood testing.
However, given the high background prevalence of type 2 diabetes in Aboriginal and Torres Strait Islander adults, AUSDRISK has limited use as a screening tool, and adults should instead proceed directly to blood testing for diabetes in conjunction with other opportunistic screening (such as for cardiovascular risk assessment – refer to Chapter 11: Cardiovascular disease prevention). Given the higher prevalence of diabetes-related complications in the Aboriginal and Torres Strait Islander population, proceeding to direct screening for diabetes has the potential to identify diabetes earlier.
Diagnosis
In diagnosing diabetes, a fasting or random blood glucose that indicates diabetes should be confirmed by retesting on a separate day, because intra-individual variation occurs. However, this may not be necessary if the patient has diabetic symptoms and a strongly positive test result.
A laboratory venous glucose test is more reliable than a capillary point-of-care test (finger prick), but the latter may sometimes be more practical and also enables further action on the same visit. An opportunistic random blood glucose is a reasonable alternative to a fasting sample, in situations where the patient is unlikely to return for a fasting test, but the ‘equivocal’ range is altered to 5.5–11 mmol/L.1
The National Vascular Disease Prevention Alliance (NVDPA) 2011 Australian guidelines state: ‘When a fasting sample is not possible, non-fasting glucose can be measured with further testing required if the result is ≥5.5 mmol/L. HbA1c can be used to diagnose diabetes with a level ≥6.5% (48 mmol/mol) being diagnostic.’13
In Australian guidelines since 2012, glycated haemoglobin (HbA1c) level ≥6.5% (48 mmol/mol) has become an acceptable method for diagnosing diabetes,14 and since 2014 has qualified for an annual Medicare Benefits Schedule (MBS) rebate.15 This rebate also applies to point-of-care ‘finger prick’ HbA1c testing in services enrolled in the Quality Assurance for Aboriginal and Torres Strait Islander Medical Services (QAAMS) pathology program.16
In remote settings, using point-of-care ‘finger prick’ HbA1c testing and, if abnormal, laboratory confirmation, has led to more rapid and accurate diagnosis of diabetes than the traditional glucose algorithm – that is, fasting glucose and confirmatory oral glucose tolerance test (OGTT).17 In children and adolescents, using HbA1c as a screening tool may underestimate the prevalence of diabetes.18
HbA1c results are affected by haemoglobin variants and alterations in red blood cell turnover (including pregnancy).19 Point-of-care HbA1c results may be less reliable than laboratory results, although the accuracy is still usually enough to rely upon for diagnosis.20 However, HbA1c results below the diagnostic threshold of 6.5% should be interpreted with caution, as HbA1c is neither sensitive nor specific for detecting prediabetes.10 There is no role for routinely testing insulin levels to assess insulin resistance.11
Behavioural interventions
The key behavioural interventions used to manage pre-diabetes are the same as those that have been shown to halve mortality in people with established type 2 diabetes when used intensively.21 For those with IGT, the Finnish Diabetes Prevention Study showed that interventions aimed at modifying weight, diet and exercise not only halved the incidence of diabetes at four years compared to a control group (number needed to treat [NNT] = 8), but maintained most of this benefit for at least three years after the initial intervention was ceased.22 There is strong evidence (level I, grade A) that lifestyle modifications that focus on weight loss, dietary change and increased physical activity should be offered to all individuals at high risk of developing type 2 diabetes.1 The large ADDITION randomised trial suggested that for newly diagnosed type 2 diabetes, ‘routine’ risk factor management is almost as effective in reducing cardiovascular events and death as intensive risk factor management.21
Dietary intervention can effectively delay or prevent diabetes. The Da Qing IGT and Diabetes Study found that, after six years, the group given specific dietary advice had a 33% reduction in the incidence of diabetes compared to the control group. Even 17 years after the study finished, follow-up data showed a 19% reduction in diabetes in the intervention group.23 Dietary recommendations are found in the Australian dietary guidelines (refer to Chapter 1: Lifestyle, ‘Overweight and obesity’).
Increasing physical activity is a particularly important and effective method of preventing diabetes. The diabetic-related benefits of regular exercise are not limited to subjects who are successful in losing weight. In the Finnish Diabetes Prevention Study, subjects who exercised for at least four hours per week but did not lose weight still had a four-fifths relative reduction in incidence of diabetes at one year compared to those who were sedentary.22 A systematic review found good evidence of a 30% reduction in diabetes for walking briskly for ≥2.5 hours per week.24 Ideally, a diabetes prevention strategy involves the combined interventions of diet modification and increased exercise. A 2017 systematic review found that lifestyle interventions were associated with a 36% reduction in relative risk of type 2 diabetes over six months to six years.10 A sevenyear follow-up study in a remote Aboriginal community involving diet and physical activity interventions found that, despite an increase in average BMI, the prevalence of IGT decreased and diabetes prevalence did not increase, possibly due to improved physical activity.25 Sedentary activities such as watching television are associated with diabetes; in Australia, those who watch television for more than 14 hours per week are 2.3 times as likely to develop new diabetes as those who watch less than 14 hours.26 Although this does not prove a direct causative effect, it is reasonable to encourage a reduction for heavy television viewers, particularly if replaced by a non-sedentary activity.
The national physical activity guidelines recommend a gradual increase in activity intensity to a goal of at least 30 minutes of moderate physical activity on most, and preferably all, days, and also have recommendations on reduced sitting time (refer to Chapter 1: Lifestyle, ‘Physical activity’).
As part of an Aboriginal and Torres Strait Islander MBS Health Assessment (item 715), a high risk of diabetes based on AUSDRISK is an eligibility criterion for referral to subsidised lifestyle programs.27 However, an AUSDRISK score of ≥12 was shown to not be a sufficiently specific threshold to prioritise referrals to lifestyle programs in a Victorian cross-sectional survey of the general population aged 40–74 years. Up to 40% of people in this study would be eligible for lifestyle programs, making the tool non-discriminatory.28 Moreover, Aboriginal and Torres Strait Islander people have fewer opportunities to use lifestyle programs due to issues with their suitability, cultural issues, family obligations, and a range of social and economic barriers that increase cardiovascular risks but also limit participation. Open access to lifestyle programs that are culturally appropriate and integrated with screening are likely to be more acceptable.29
Chemoprophylaxis and surgery
Current National Health and Medical Research Council (NHMRC) guidelines state that, as many of the medications used in diabetes prevention studies have established side effects, potential benefits and harms should be taken into account before considering pharmacotherapy.1
Oral hypoglycaemic medication at the pre-diabetic stage can delay or prevent progression to diabetes. A meta-analysis of 31 randomised trials in people at risk of diabetes showed metformin improves weight, lipid profiles and insulin resistance, and reduces new-onset diabetes by 40%.30 Despite these promising results, metformin appears to be less effective than lifestyle changes. A large US trial randomised subjects with pre-diabetes into an intensive lifestyle modification program, metformin, or placebo.31 At three years, the metformin group had a 31% relative risk reduction in onset of diabetes compared to placebo (NNT = 13.9). However, the lifestyle changes group showed a significantly larger relative risk reduction of 58% (NNT = 6.9) across all ages and ethnic groups. The trial was prematurely discontinued on the basis that it was unethical not to offer all participants the intensive lifestyle program.
A Cochrane review showed that acarbose reduces the incidence of type 2 diabetes by 25% (NNT=10) in patients with IGT.32 A study randomising subjects with obesity into receiving lifestyle advice plus either orlistat (a weight loss agent) or placebo found that, in the subgroup who had IGT at baseline, orlistat gave a 45% risk reduction of progression to diabetes at four years.33 However, a high number discontinued therapy: 48% of the orlistat group, and 66% of the control group.
Surgical weight loss interventions for severe obesity can result in a dramatic reduction in diabetes. The Swedish Obese Subjects study compared subjects who had bariatric surgery with matched controls. At two years, the 1845 surgery cases had a 32-fold reduction in incidence of newly diagnosed diabetes.34 At eight years, the prevalence of diabetes in the surgery group remained unchanged from baseline, but had tripled (from 7.8% to 24.9%) in the matched controls.35 A prospective study of 30 obese Aboriginal adults diagnosed with diabetes who underwent gastric banding found that 66% had diabetes remission at two years.36 (Refer to Chapter 1: Lifestyle, ‘Overweight and obesity’ for a more detailed review of surgical weight loss interventions.)
All people at risk for diabetes should be offered lifestyle advice encouraging increased physical activity and improved dietary intake, and advised as to the benefits of weight loss. People who are morbidly obese and potentially suitable for bariatric surgery should be encouraged to consider surgical referral, if available.
Environmental
In remote and rural areas, poor food supply undermines efforts to address the poor nutritional status of Aboriginal and Torres Strait Islander peoples. Community stores are frequently the only food source outside traditional ‘bush’ food.37 Various programs to influence the quality and cost of high-nutritional foods in community stores have had some success; a retail cooperative in Arnhem land provided 100% freightsubsidised fruit and vegetables and doubled the intake of these foods per person at three years.38 An analysis of 29 years of community store interventions in remote South Australia found that some schemes successfully improved access to healthy, fresh foods, but overall diet quality had worsened over time.39
Surveys in many remote and rural Aboriginal communities have shown facilities for sporting and recreational activities are lacking, yet these are a high priority for community members.40 (Refer to Chapter 1: Lifestyle, ‘Overweight and obesity’.)
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