What is the value for abnormal 1-hour glucose (glucose) tolerance?

From the Guidelines

An abnormal 1-hour glucose value during a glucose tolerance test is typically considered to be 180 mg/dL (10.0 mmol/L) or higher. This threshold is commonly used in the diagnosis of gestational diabetes during pregnancy, where pregnant women undergo a glucose challenge test. After consuming a 50-gram glucose solution, blood glucose is measured at the 1-hour mark. If the result exceeds this threshold, further testing with a 3-hour glucose tolerance test is usually recommended to confirm the diagnosis. The elevated glucose level indicates that the body is not processing glucose efficiently, suggesting insulin resistance or insufficient insulin production. This impaired glucose metabolism can lead to hyperglycemia, which may require dietary modifications, exercise, or medication to manage. It's essential to note that interpretation should always be done by a healthcare provider, as specific thresholds may vary slightly between different healthcare systems or for different patient populations. According to the most recent study 1, the diagnosis of gestational diabetes is made when at least two of the following four plasma glucose levels are met or exceeded: fasting, 95 mg/dL; 1 hour, 180 mg/dL; 2 hours, 155 mg/dL; and 3 hours, 140 mg/dL.

Some key points to consider:

• The 1-hour glucose threshold of 180 mg/dL is a commonly used cutoff for diagnosing gestational diabetes 1.
• The diagnosis of gestational diabetes is typically made using a 2-step approach, involving an initial glucose challenge test followed by a 100-g oral glucose tolerance test if the initial result is abnormal 1.
• The American College of Obstetricians and Gynecologists (ACOG) notes that one elevated value can be used for diagnosis, but this may vary depending on the specific clinical context 1.
• It's crucial to consider the potential risks and benefits of screening and diagnosis, as well as the impact on maternal and fetal outcomes 1.
• The Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study provided valuable insights into the relationship between glucose levels and pregnancy outcomes, informing the development of new diagnostic criteria for gestational diabetes 1.

Overall, the diagnosis and management of gestational diabetes require careful consideration of individual patient factors, as well as the latest evidence-based guidelines and recommendations.

From the Research

Abnormal 1-hour Glucose Tolerance Values

• The value for abnormal 1-hour glucose tolerance is typically considered to be 140 mg/dl or greater 2, 3, 4, 5, 6
• However, some studies suggest that a value of 182 mg/dl or greater may be a more accurate cutoff for predicting gestational diabetes 2
• A study published in 2001 found that the rate of abnormal glucose levels measured after 1 hour (>140 mg%) was significantly higher than the rate of abnormal glucose levels measured after 2 hours (>120 mg%) postprandially in women with gestational diabetes mellitus (GDM) 3
• Another study published in 2013 found that glucose challenge test values of 140 mg/dl or more were associated with an increase in odds of the composite perinatal outcome, large for gestational age (LGA), and macrosomia 5
• A retrospective cohort study published in 2025 found that an isolated abnormal 1-hour glucose challenge test (GCT) among patients without gestational diabetes (GDM) was associated with adverse outcomes, including an increased risk for the composite perinatal morbidity outcome, cesarean, and hypertensive disorders of pregnancy 6

Comparison of 1-hour and 2-hour Glucose Measurements

• A study published in 1998 compared 2-hour postprandial glucose measurements with the standard 1-hour, 50 gm glucola screen as a predictor of gestational diabetes, and found that the 1-hour glucose screen was more predictive of gestational diabetes than the postmeal assessment 2
• A study published in 2001 compared the rate of abnormal glucose levels measured after 1 hour (>140 mg%) with those measured after 2 hours (>120 mg%) postprandially in women with gestational diabetes mellitus (GDM), and found that the rate of abnormal values was 2.5-fold greater 1 hour postbreakfast than 2 hours postbreakfast 3

Glycohemoglobin Determination and 1-hour Oral Glucose Screen

• A study published in 1982 evaluated the use of glycohemoglobin (HbA1) as a screening tool for the detection of gestational diabetes, and found that the combination of two abnormal tests, glucose screen and HbA1, predicted gestational diabetes in only four of 15 (27%) of the patients 4