What is the purpose of a mixed meal glucose tolerance test (GTT) to assess reactive hypoglycemia?

From the Guidelines

A mixed meal glucose tolerance test (GTT) is the preferred method to assess reactive hypoglycemia, as it provides a more physiological stimulation test for the detection of postprandial hypoglycemia. The test involves having the patient consume a mixed meal containing carbohydrates, fats, and proteins after an overnight fast, and then measuring blood glucose concentrations, as well as other parameters such as haematocrit and pulse rate, at 30-min intervals for up to 2 hours after ingestion 1.

Key Considerations

• The mixed meal tolerance test is considered positive for late dumping syndrome in patients who develop hypoglycemia between 60 and 180 min after meal ingestion 1.
• The test should be conducted in a clinical setting where symptoms can be monitored and addressed if severe hypoglycemia occurs.
• Patients should fast overnight before the test, avoid caffeine and alcohol for 24 hours prior, and discontinue medications that might affect glucose metabolism (with physician guidance).

Advantages of the Mixed Meal GTT

• The mixed meal tolerance test holds promise as a more physiologic stimulation test for the detection of post-gastric bypass hypoglycemia, with improved specificity in asymptomatic patients 1.
• The test mimics normal eating patterns and triggers a more natural insulin response, making it a more accurate reflection of real-world postprandial glucose dynamics than other provocative testing methods.

Limitations and Future Directions

• Further validation of the mixed meal tolerance test is needed in patients with and without hypoglycemia symptoms, as well as in healthy individuals, to establish normative values 1.
• The diagnostic accuracy of the oral glucose tolerance test (OGTT) is low, and normative values have not been firmly established, leading to clinical practice guidelines not supporting its use for diagnosing postprandial hypoglycemia 1.

From the Research

Purpose of Mixed Meal Glucose Tolerance Test (GTT)

The purpose of a mixed meal glucose tolerance test (GTT) is to assess reactive hypoglycemia in a more natural and physiologic manner compared to the oral glucose tolerance test (OGTT) [ 2, 3,4 ].

Key Findings

• A mixed meal test is used to diagnose reactive hypoglycemia, as it mimics daily dietary experiences and can help identify patients who experience hypoglycemic symptoms after eating 3, 4.
• The mixed meal test is considered a more accurate assessment of reactive hypoglycemia than the OGTT, as it induces hypoglycemia less frequently in subjects without insulinomas 3.
• Studies have shown that the mixed meal test can help identify patients with reactive hypoglycemia, particularly those with symptoms suggestive of postprandial hypoglycemia 4, 5.

Comparison with Other Tests

• The oral glucose tolerance test (OGTT) is not specific for diagnosing postprandial reactive hypoglycemia, as it can induce low blood glucose values in subjects without symptoms 5.
• A standardized hyperglucidic breakfast test has been shown to be effective in detecting reactive hypoglycemia, with a higher frequency of low blood glucose values in subjects with postprandial symptoms 5.

Clinical Implications

• The mixed meal test can be used to diagnose reactive hypoglycemia and to monitor blood glucose and insulin levels in patients with symptoms suggestive of postprandial hypoglycemia 2, 4.
• The test can help identify patients who are susceptible to reactive hypoglycemia and may be used to develop personalized treatment plans 6.