Prediabetes: proactive intervention to prevent or delay onset of type 2 diabetes

Type 2 diabetes is recognised as a major health problem in Australia and yet about 60% of cases are preventable through lifestyle interventions.¹ Recently, the major diabetes professional societies – Australian Diabetes Society, Australian Diabetes Educators Association, Dietitians Association of Australia, Exercise and Sports Science Australia and Pharmaceutical Society of Australia – reviewed the pertinent evidence and developed consensus-based clinical recommendations on the management of prediabetes.² It is their position that the early detection of prediabetes represents a crucial step for initiating proactive intervention and support strategies to prevent or delay the onset of type 2 diabetes and associated comorbidities, including cardiovascular disease (CVD). This article discusses the major points of this position statement and provides a summary of the recommendations (Box).² 

Defining prediabetes 

Prediabetes is a metabolic condition characterised by elevated blood glucose levels, but not to the diagnostic threshold for type 2 diabetes (Flowchart).² It may include impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and/or elevated glycated haemoglobin (HbA_1c). Prediabetes affects nearly one in six Australian adults (more than 2 million individuals) over the age of 25 years.³ Without intervention, about one in three people with prediabetes will develop type 2 diabetes within 10 years.² Furthermore, people with prediabetes are at greater risk of developing CVD than those without prediabetes.²

Screening and detection of prediabetes

AUSDRISK screening tool

Prediabetes can be identified through the screening pathway for type 2 diabetes. The Australian Type 2 Diabetes Risk Assessment (AUSDRISK) screening tool is a short questionnaire designed to estimate the risk of progression to type 2 diabetes over five years in individuals based on clinical risk factors, including age, gender, ethnicity, family history of diabetes, previous history of high blood glucose levels or blood pressure, waist measurement and lifestyle factors.⁴ Individuals who are at intermediate risk (score of 6 to 11) or high risk (score of 12 or above) should undergo biochemical testing to identify prediabetes or type 2 diabetes (see Flowchart).² 

Pathology screening

Prediabetes and type 2 diabetes can be identified by: 

• two-hour oral glucose tolerance test (OGTT)
• measurement of fasting blood glucose levels
• HbA_1c. 

Each of these tests has its benefits and limitations and therefore the most appropriate test should be tailored to the individual and planned intervention. An OGTT is the most burdensome for patients but is the only test that can distinguish between IFG and IGT. As the strongest evidence of benefit for intensive, structured lifestyle programs is for people with IGT, it may be important to identify IGT using an OGTT before referral to such a program. A fasting glucose measurement only involves a single timepoint so may be more convenient for patients, but can only identify IFG, not IGT, so may misclassify some patients as not having prediabetes. In practice, an HbA_1c test may be most practical as it is a single timepoint test that does not require fasting. However, the HbA_1c test cannot distinguish between IFG and IGT, only an overall elevated glycaemia. HbA_1c test can be unreliable in people who have conditions in which red cell turnover or haemoglobin binding of glucose is abnormal (e.g. haemoglobinopathies, anaemia, iron deficiency, and significant renal impairment). 

Management of prediabetes 

The management of prediabetes should be individualised and multifaceted, and involve a multidisciplinary team of healthcare professionals. There is strong evidence to support intensive and structured lifestyle programs (i.e. preset curriculum and schedule of visits) for individuals with IGT, but less certain for those with IFG.² Regardless, lifestyle interventions are recommended for all individuals with prediabetes.^5-7 The goal of a management plan is to reverse prediabetes, or at least delay onset of type 2 diabetes, and reduce associated risk factors through weight reduction, healthy eating, regular physical activity, stress reduction/improved sleep and smoking cessation, as appropriate. Lifestyle interventions in individuals with overweight or obesity that result in a weight loss of 5 to 7% reduce the risk of developing type 2 diabetes by 57%, with a further reduction in those that sustained a weight loss of 5% after three years.^8,9 Patient-centred care and shared decision-making are important for ensuring the management plan is tailored to the individuals’ goals, preferences and readiness to make behaviour modifications to encourage long-term adoption of lifestyle changes.⁵

Healthy eating

Dietary advice for individuals with prediabetes should be consistent with the Australian Dietary Guidelines,¹⁰ which provide evidence-based nutrition advice, but are flexible enough to encompass a range of healthy eating approaches. Long-term weight loss/weight maintenance is more likely to be achieved with realistic and sustainable dietary approaches and a focus on macronutrient quality. Meta-analysis of various dietary approaches suggests value in a range of evidence-based diets including Mediterranean, lower carbohydrate, lower glycaemic index and higher protein diets.¹¹ An accredited practising dietitian can provide individualised dietary advice and support.

Physical activity

Regular physical activity and exercise should be part of the therapeutic strategy in people with prediabetes, given the improvements in glucose control, cardiovascular risk factors, mood and sleep.^12-15 Ideally, 150 to 300 minutes of moderate to vigorous intensity aerobic and resistance exercise should be undertaken each week, with no more than two consecutive days without exercising.^13,16,17 Further benefit may be obtained with additional exercise or exercise completed at higher intensities. In addition, strong evidence supports reducing overall sedentary time and interrupting prolonged sitting.^18-20 Individuals with prediabetes should be referred (where feasible) to an accredited exercise physiologist or physiotherapist to design an individualised exercise prescription.

Pharmacotherapy

No medications have a TGA indication for the prevention of type 2 diabetes. Oral glucose-lowering agents, such as metformin, are generally not as effective as an intensive lifestyle intervention. Therefore, if oral antihyperglycaemic agents are used, it is recommended that they are prescribed in conjunction with intensive lifestyle modification. Pharmacotherapy is likely to be most beneficial in younger adults, as the long-term benefits of a delay in onset of type 2 diabetes would be the greatest in this group.²¹

Psychosocial care

Individuals with prediabetes are at a higher risk of depression and anxiety.²² Psychological distress may reduce the capacity for people with type 1 or 2 diabetes to engage in daily health behaviours, including healthy eating and physical activity.²² Ongoing psychological care may be considered through regular, supportive interactions with the GP and multidisciplinary team, plus referral of the patient to a counsellor, psychologist or psychiatrist as appropriate.

Creating a holistic prediabetes management plan

The management plan for people with prediabetes should be multifaceted and individualised and include healthy eating and physical activity. As there are several different lifestyle approaches that have been proven to be effective in people with prediabetes, management should be patient-centred and advice (e.g. on healthy eating, exercise strategies or clinical targets) should be consistent between healthcare professionals. 

The frequency of ongoing monitoring needs to be individualised. There is no indication for self-monitoring of capillary blood glucose levels by individuals with prediabetes but annual retesting of HbA_1c to screen for type 2 diabetes is recommended and supported by Medicare. Other health outcomes, such as weight, lipid and blood pressure management, should be assessed by the multidisciplinary team in conjunction with the individual to assess the efficacy of interventions and disease progression. Ongoing support from the GP and other healthcare professionals, and regular interactions, are encouraged to build on strong, supportive, lasting professional relationships with patients, as well as providing education and advice. Education on prevention of type 2 diabetes and healthy lifestyle advice is best provided at first identification of prediabetes, and as frequently as needed or desired to support behavioural or pharmacological interventions.

Lifestyle programs may be provided by referring the individual to allied healthcare professionals, such as accredited practising dietitians or accredited exercise physiologists. Programs can also be provided by public, private or community organisations with expertise in the management of prediabetes (via face-to-face meetings, telephone, webinars or community programs). For example, the NSW Government telephone-based Get Healthy: type 2 diabetes prevention program (see: www.gethealthynsw.com.au/program/type-2-diabetes-prevention-program/) or Diabetes Australia state and territory-run programs (see: www.diabetesaustralia.com.au/prevention for further details). A Medicare chronic disease plan management is not available to people with prediabetes alone.         ET

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