- Impaired glucose tolerance is defined as a fasting plasma glucose concentration of less than 7.0 mmol/L with a two-hour oral glucose tolerance test value of 7.8 to 11.1 mmol/L.
- Impaired fasting glycaemia is defined as a fasting glucose of 6.1 to 6.9 mmol/L.
- The World Health Organization (WHO) has recommended that people with an HbA1c of 42−47 mmol/mol (6.0-6.5%) are at high risk of diabetes.
Impaired glucose tolerance, typically characterised by hyperglycaemia and insulin resistance, is considered to be a stage in the development of type 2 diabetes mellitus and a risk factor for cardiovascular disease. Therefore, impaired glucose tolerance is often referred to as pre-diabetes.
- The prevalence of impaired glucose tolerance increases linearly from about 15% in middle age to 35-40% in the elderly.
- Evidence suggests that a 1 kg/m2 increase in body mass index (BMI) increases the risk of developing new-onset type 2 diabetes by 8.4%. The risk of impaired fasting glucose rises by 9.5%.
- A first-degree relative with diabetes.
- Ethnicity: South Asian, Chinese, African-Caribbean and black African.
- Increasing age.
- Level of deprivation in the area where someone lives.
- Patients with impaired glucose tolerance are usually asymptomatic.
- Features of related risk factors for cardiovascular disease may be present, even with a mild degree of hyperglycaemia. They include hypertension, obesity, dyslipidaemia and macrovascular disease, such as stroke, coronary disease or peripheral arterial disease.
- Glucose control:
- Fasting blood glucose.
- Glycosylated haemoglobin.
- Oral glucose tolerance test.
- Other investigations similar to those for people with type 2 diabetes may be indicated.
- It has been shown that the risk of progression from impaired glucose tolerance to type 2 diabetes mellitus can be reduced by lifestyle interventions.
- Several clinical trials have found that lifestyle modification is the most effective strategy to prevent progression to type 2 diabetes.
- The advice is essentially the same as diet and exercise advice in diabetes:
- Weight reduction, if appropriate.
- Reduction in total intake of fat and intake of saturated fat.
- Increasing intake of dietary fibre.
- Increasing physical activity.
The risk reduction of diabetes using metformin, pioglitazone, acarbose, valsartan and orlistat in clinical studies has ranged from 14% to 72%.
- Reversal of drug-related iatrogenic causation of glucose intolerance. Whenever possible, substitute agent(s) that do not have an adverse effect on glucose tolerance, or reduce the dosage of the offending drug - eg, replacing a thiazide diuretic when treating hypertension, minimising use of corticosteroids.
- Metformin should be considered for adults at high risk whose blood glucose measure (fasting plasma glucose or HbA1c) shows they are still progressing towards type 2 diabetes, despite their participation in an intensive lifestyle-change programme, or if they are unable to participate in lifestyle-change programmes because of a disability or for medical reasons.
- Orlistat should be considered for adults who have a BMI of 28.0 kg/m2 or more and whose blood glucose measure (fasting plasma glucose or HbA1c) shows they are still progressing towards type 2 diabetes, especially those who are not benefiting from lifestyle-change programmes, or who are unable to participate in physical activity because of a disability or for medical reasons.
- There has been some evidence that angiotensin-converting enzyme (ACE) inhibitors may have a role in preventing diabetes, especially for those with other cardiovascular risk factors.
National Institute for Health and Care Excellence (NICE) guidance
- High risk groups:
- People of South Asian, Chinese, African-Caribbean, black African and other high-risk black and minority ethnic groups.
- People with conditions that increase the risk of type 2 diabetes.
- High risk of type 2 diabetes (fasting blood glucose 5.5-6.9 mmol/L) or HbA1c 42-47 mmol/mol (6.0-6.4%):
- Offer an intensive lifestyle change programme to increase physical activity, to achieve and maintain weight loss and to increase dietary fibre and reduce fat intake, particularly saturated fat.
- Reassess weight and BMI and offer a blood test for fasting blood glucose or HbA1c at least once a year.
- Consider for adults at high risk whose blood glucose measurement (fasting plasma glucose or HbA1c) shows they are still progressing towards type 2 diabetes, despite their participation in an intensive lifestyle-change programme, or adults at high risk who are unable to participate in lifestyle-change programmes because of a disability or for medical reasons.
- Continue to offer advice on diet and physical activity along with support to achieve their lifestyle and weight-loss goals.
- Check the person's renal function before starting treatment, and then twice yearly (more often if they are older or if deterioration is suspected).
- Start with a low dose (for example, 500 mg once daily) and then increase gradually as tolerated, to 1500-2000 mg daily. If the person is intolerant of standard metformin, consider using modified-release metformin.
- Prescribe metformin for 6-12 months initially. Monitor the person's fasting plasma glucose or HbA1c levels at three-monthly intervals and stop the drug if no effect is seen.
- Orlistat should be considered for adults who have a BMI of 28.0 kg/m2 or more, whose blood glucose measurement (fasting plasma glucose or HbA1c) shows they are still progressing towards type 2 diabetes. In particular, this includes those who are not benefiting from lifestyle-change programmes, or who are unable to
participate in physical activity because of a disability or for medical reasons.
- Approximately 40-50% of individuals with impaired glucose tolerance will progress to type 2 diabetes over their lifetime.
- Impaired glucose tolerance is associated with an increased risk of cardiovascular disease.
- The precise relationship between impaired glucose tolerance and microvascular complications is less certain.
- Avoid being overweight and eat a healthy diet, with high fibre, low fat and lots of fruit and vegetables.
- Encourage regular physical activity.
Further reading and references
; World Health Organization/International Diabetes Federation, 2006
; NICE Public Health Guidance (May 2011)
; JBS3, 2014
; ESC Guidelines on diabetes, pre-diabetes, and cardiovascular diseases developed in collaboration with the EASD: the Task Force on diabetes, pre-diabetes, and cardiovascular diseases of the European Society of Cardiology (ESC) and developed in collaboration with the European Association for the Study of Diabetes (EASD). Eur Heart J. 2013 Oct34(39):3035-87. doi: 10.1093/eurheartj/eht108. Epub 2013 Aug 30.
; NICE Public Health Guidance (July 2012)
; Predictors of lifestyle intervention outcome and dropout: the SLIM study. Eur J Clin Nutr. 2011 Oct65(10):1141-7. doi: 10.1038/ejcn.2011.74. Epub 2011 May 18.
; Non-pharmacological interventions to reduce the risk of diabetes in people with impaired glucose regulation: a systematic review and economic evaluation. Health Technol Assess. 2012 Aug16(33):1-236, iii-iv. doi: 10.3310/hta16330.
; Association between change in daily ambulatory activity and cardiovascular events in people with impaired glucose tolerance (NAVIGATOR trial): a cohort analysis. Lancet. 2013 Dec 19. pii: S0140-6736(13)62061-9. doi: 10.1016/S0140-6736(13)62061-9.
; Pharmacological strategies for preventing type 2 diabetes in patients with impaired glucose tolerance. Drugs Today (Barc). 2013 Aug49(8):499-507. doi: 10.1358/dot.2013.49.8.2002839.
; Angiotensin receptor blockers for prevention of new-onset type 2 diabetes: a meta-analysis of 59,862 patients. Int J Cardiol. 2012 Mar 8155(2):236-42. doi: 10.1016/j.ijcard.2010.10.011. Epub 2010 Oct 30.
; Type 2 diabetes can be prevented with early pharmacological intervention. Diabetes Care. 2011 May34 Suppl 2:S202-9. doi: 10.2337/dc11-s221.
; Relationship between glycated haemoglobin and microvascular complications: is there a natural cut-off point for the diagnosis of diabetes? Diabetologia. 2009 Jul52(7):1279-89. doi: 10.1007/s00125-009-1360-5. Epub 2009 Apr 22.