What are the next steps for a patient with an abnormal 1-hour Glucose Tolerance Test (GTT)?

From the Guidelines

If you have an abnormal 1-hour glucose tolerance test (GTT) during pregnancy screening, the next step is to undergo a 3-hour diagnostic GTT to confirm or rule out gestational diabetes, as recommended by the most recent guidelines 1. The 3-hour test involves fasting overnight, having blood drawn for a fasting glucose level, drinking a 100-gram glucose solution, and then having blood drawn at 1,2, and 3 hours afterward.

• The diagnosis of gestational diabetes is made if two or more values exceed the thresholds of fasting ≥92 mg/dL, 1-hour ≥180 mg/dL, and 2-hour ≥153 mg/dL, as outlined in the 2025 standards of care in diabetes 1.
• If diagnosed, treatment typically begins with dietary modifications and blood glucose monitoring.
• If glucose targets aren't met with lifestyle changes, medication may be needed, typically starting with insulin or sometimes metformin. The 3-hour GTT is necessary because the 1-hour test is a screening tool with high sensitivity but lower specificity, meaning it catches most cases but has false positives, which is why confirmation with the more definitive 3-hour test is required before diagnosis and treatment, as supported by the American Diabetes Association guidelines 1.

From the Research

Abnormal 1 Hour GTT Results

If a patient has an abnormal 1 hour glucose tolerance test (GTT) result, the next steps may involve:

• Further testing to confirm the diagnosis of pre-diabetes or diabetes
• Evaluation of the patient's risk factors for metabolic syndrome, such as high blood pressure, high cholesterol, and obesity 2
• Consideration of the patient's hemoglobin A1c (HbA1c) level to determine the best course of action for diagnosis and treatment 3, 4, 5, 6

Diagnostic Criteria

The diagnostic criteria for pre-diabetes and diabetes using the 1 hour GTT and HbA1c levels are:

• 1 hour GTT: 155-199 mg/dL for impaired glucose tolerance (IGT) 2
• HbA1c: 5.7-6.4% for pre-diabetes and ≥6.5% for diabetes 4, 5, 6
• Optimal HbA1c cutoff points for prediabetes and diabetes may vary depending on body mass index (BMI) classification 6

Next Steps

The next steps for a patient with an abnormal 1 hour GTT result may include:

• A 2 hour GTT to confirm the diagnosis of pre-diabetes or diabetes 3
• Measurement of HbA1c level to determine the best course of action for diagnosis and treatment 4, 5, 6
• Evaluation of the patient's risk factors for metabolic syndrome and consideration of lifestyle modifications or pharmacological interventions to reduce the risk of developing type 2 diabetes and cardiovascular disease 2