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- March 10, 2010 |
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| Presentation |
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"IFG and IGT - State of the Art"Dr. Nigel Unwin (biography)
English - 2005-04-14 - 32 minutes
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 | (25 slides) |
Summary :
Impaired glucose tolerance (IGT) and impaired fasting glycaemia (IFG) represent higher than normal blood glucose levels, based on post glucose challenge and fasting blood measurement respectively, and are associated with a markedly increased risk of developing diabetes and an increased risk of cardiovascular disease. Interest in these categories has grown with the clear demonstration that lifestyle and pharmacological interventions in men and women with IGT substantially reduces the risk of diabetes. Partly for this reason the term "prediabetes" is often used to describe IFG and IGT.
This presentation focuses on IFG and IGT as defined by the American Diabetes Association in 1997 and the World Health Organization in 1999. These conditions are common in most populations studied, being present in 10 to over 30% of adults depending on the population and age group. In the majority of populations studied, IGT is more prevalent than IFG, and there is a difference in phenotype and gender distribution between the two categories. The prevalence of IFG tends to plateau in middle age whereas the prevalence of IGT rises into old age; and IFG tends to be substantially more common among men and IGT slightly more common among women. Therefore, it is not surprising that the concordance between the categories of IFG and IGT is low, and usually less than half of people with IFG have IGT, and even a lower proportion (20-30%) with IGT also have IFG. However, both isolated IFG and IGT (I-IFG, I-IGT) are associated with a substantially increased risk of developing diabetes, with the highest risk in people with combined IFG and IGT. Because IGT is commoner than IFG in most populations it is more sensitive (but slightly less specific) for identifying people who will develop diabetes. In most populations studied, 60% of people who develop diabetes have either IGT or IFG 5 years or so before, with the other 40% having normal glucose tolerance at that time.
The relatively limited published data on insulin resistance and secretion in I-IFG and I-IGT, and on their association with cardiovascular risk factors are somewhat conflicting. These differences may represent differences in the populations studied and differences in methodology. At present it is reasonable to conclude that when insulin sensitivity is measured directly, I-IGT is a more insulin resistant state than I-IFG and in the latter a defect in early insulin secretion is characteristic. Data on their association with cardiovascular risk factors suggest they tend to be higher in I-IGT although some studies have found little difference. In unadjusted analyses both IFG and IGT are associated with CVD and total mortality. In separate analyses for fasting and 2-HPG adjusted for other cardiovascular risk factors (from the DECODE study) there remains a continuous relationship between 2-HPG and mortality, but an independent relationship with fasting glucose is only found above 7.0 mmol/l. However, more studies on cardiovascular disease events and overall mortality associated with these conditions are needed.
Finally in 2003 a lowering of the cut point for IFG was proposed by the American Diabetes Association, from a plasma glucose of 6.1 to 5.6 mmoll-1. The rationale for this was to improve the prediction of the future development of diabetes and to increase the proportion of people with IGT who also have IFG. This change remains controversial. It increases the prevalence of IFG by 2 to greater than 3 fold, and identifies individuals with lower levels of cardiovascular risk factors. Whether individuals so identified would benefit from interventions remains unclear. At the present time the World Health Organization's cut point for IFG remains unchanged from that recommended in 1999.
Learning objectives :
After viewing this presentation the participant will be able to discuss:
- Epidemiology of IFG and IGT
- Metabolic characteristics and CV risk factors associated with IFG and IGT
- Risk of diabetes and CVD mortality associated with IFG and IGT
- ADA proposal to lower the cut point for IFG
Bibliographic references :
M Coutinho, HC Gerstein, Y Wang and S Yusuf. The relationship between glucose and incident cardiovascular events. A metaregression analysis of published data from 20 studies of 95,783 individuals followed for 12.4 yearsDiabetes Care. 1999;22(2):233-240.
Andreas Festa, Ralph D’Agostino, Jr., Anthony J.G. Hanley, Andrew J. Karter, Mohammed F. Saad, and Steven M. Haffner. Differences in Insulin Resistance in Nondiabetic Subjects With Isolated Impaired Glucose Tolerance or Isolated Impaired Fasting Glucose Diabetes 53:1549-1555, 2004.
The DECODE Study Group Age- and Sex-Specific Prevalences of Diabetes and Impaired Glucose Regulation in 13 European CohortsDiabetes Care 26:61-69, 2003.
N. Unwin, J. Shaw, P. Zimmet and K. G. M. M. Alberti. Impaired glucose tolerance and impaired fasting glycaemia: the current status on definition and intervention Diabetic Medicine. Volume 19 Issue 9 Page 708 - September 2002.
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