What are the results of the insulin response to glucose tolerance test?

From the Guidelines

Insulin response to glucose tolerance testing is critical for diagnosing and managing diabetes, with abnormal responses indicating potential metabolic disorders such as insulin resistance, prediabetes, or diabetes, as outlined in the 2021 standards of medical care in diabetes 1.

Insulin Response and Glucose Tolerance

The insulin response to a glucose tolerance test provides valuable information about how the body processes sugar. A normal response involves a rapid increase in insulin levels after glucose consumption, peaking within 30-60 minutes, and then gradually returning to baseline as blood sugar normalizes.

Abnormal Insulin Response

An abnormal insulin response, characterized by either excessive insulin production (hyperinsulinemia) or insufficient production (hypoinsulinemia), may indicate metabolic disorders. According to the criteria defining prediabetes, a 2-hour plasma glucose level during a 75-g oral glucose tolerance test (OGTT) between 140 mg/dL and 199 mg/dL is indicative of impaired glucose tolerance (IGT) 1.

Interpretation and Recommendations

For proper interpretation, fasting insulin levels should be considered in the context of the glucose tolerance test results. The American Diabetes Association (ADA) recommends screening for prediabetes and type 2 diabetes risk through an informal assessment of risk factors or with an assessment tool, such as the ADA risk test, to guide providers on whether performing a diagnostic test is appropriate 1.

Management and Treatment

In cases of abnormal insulin response or diagnosed diabetes, management strategies may include lifestyle modifications such as diet changes, regular exercise, and weight management. Medications like metformin may be prescribed for significant insulin resistance or diabetes, with typical starting doses of 500mg daily, potentially increasing to 2000mg daily in divided doses, as part of a comprehensive treatment plan 1. Understanding and addressing insulin response issues early on can help prevent the progression to more serious conditions like type 2 diabetes or metabolic syndrome.

From the Research

Insulin Response to Glucose Tolerance Test

The results of the insulin response to glucose tolerance test can be summarized as follows:

• Insulin sensitivity increased in individuals with impaired glucose tolerance (IGT) and normal glucose tolerance (NGT) after lifestyle intervention, with a 9% increase in IGT and 17% increase in NGT 2.
• Glucose effectiveness, the ability of glucose to stimulate its own uptake and suppress its own production, plays a significant role in regulating glucose tolerance, especially in conditions of declining insulin secretion and action 3.
• In patients with newly diagnosed type 2 diabetes, short-term insulin glargine plus oral hypoglycemic agents (OHAs) may be an alternative to continuous subcutaneous insulin infusion (CSII) for initial intensive therapy, with comparable effects on glycemic control and beta-cell function 4.
• Insulin sensitivity during an oral glucose tolerance test (OGTT) can be improved with metformin and thiazolidinedione, with a significant increase in insulin sensitivity in dynamic conditions (OGIS) and a tendency towards improvement in total insulin secretion over the OGTT 5.
• A fixed combination of metformin and pioglitazone can provide greater improvement in insulin resistance than metformin alone and similar changes in insulin resistance to dapagliflozin in patients with newly diagnosed type 2 diabetes 6.

Key Findings

• Lifestyle intervention can improve insulin sensitivity in both IGT and NGT individuals.
• Glucose effectiveness is an important factor in regulating glucose tolerance.
• Insulin glargine plus OHAs can be an alternative to CSII for initial intensive therapy in newly diagnosed type 2 diabetes.
• Metformin and thiazolidinedione can improve insulin sensitivity during an OGTT.
• A fixed combination of metformin and pioglitazone can provide greater improvement in insulin resistance than metformin alone.

Parameters of Glucose Metabolism

• Insulin sensitivity: increased in IGT and NGT individuals after lifestyle intervention 2, improved with metformin and thiazolidinedione 5, and improved with a fixed combination of metformin and pioglitazone 6.
• Glucose effectiveness: plays a significant role in regulating glucose tolerance, especially in conditions of declining insulin secretion and action 3.
• Beta-cell function: improved with short-term insulin glargine plus OHAs 4 and with a fixed combination of metformin and pioglitazone 6.