What is the clinical importance of differentiating between impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) states?
What are some key differences in management of IGT vs IFG?
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IGT and IFG are different phenotypes of prediabetes. Clinical studies* suggest that IGT may be associated with higher cardiovascular risk than IFG. The molecular mechanisms and the treatments are thus different. IGT, which is due to impairments of beta cell insulin release, can be treated with reduction of carbohydrate intake. IFG, which is due to increased hepatic glucose production during the night, can be treated with weight loss which can improve insulin sensitivity. If medications are used, GLP-1 drugs can help with both conditions. IFG should respond to metformin, which specifically reduces hepatic glucose production.
Just to define, IFG is diagnosed by a fasting plasma glucose of 100-125mg/dl and impaired glucose tolerance by a 2-hour glucose value of 140-199 mg/dl after a glucose load. I agree with Dr. @Dr. First Last that the CV risk may be higher with IGT compared to IFG. Either of these criteria may be used to diagnose to diagnose "prediabetes'. Frequently, the two may coexist. I also believe that both IFG and IGT will improve with weight loss. At present, no drug, including Metformin is approved by the FDA for the treatment of prediabetes. However, ADA has suggested that the use of Metformin may be considered in specific situations for the treatment of prediabetes.