Normal 1-Hour Post-Load Glucose Value After 75g OGTT
The normal 1-hour plasma glucose value after a 75-gram OGTT is less than 180 mg/dL (10.0 mmol/L), with values ≥180 mg/dL indicating gestational diabetes in pregnancy or increased risk for future diabetes in non-pregnant individuals. 1
Context-Specific Normal Values
For Gestational Diabetes Screening
- The diagnostic threshold is 180 mg/dL (10.0 mmol/L) - any value at or above this level indicates gestational diabetes when using the one-step approach 1
- This threshold is based on the HAPO study, which demonstrated continuous increases in adverse pregnancy outcomes (birthweight >90th percentile, cesarean delivery, neonatal hypoglycemia) as 1-hour glucose rises 1
- The International Association of Diabetes and Pregnancy Study Groups (IADPSG) established this cutoff based on pregnancy outcome data rather than future diabetes risk 1
For Non-Pregnant Adults
- Values <155 mg/dL are considered normal in most populations, as this threshold distinguishes individuals at low versus high risk for developing type 2 diabetes 2, 3
- Research from Japanese populations suggests 179-180 mg/dL as the upper limit of normal, with values ≥179 mg/dL associated with 26.9% diabetes prevalence versus 0.5% in those below this threshold 4
- Values ≥155 mg/dL in individuals with otherwise normal glucose tolerance are associated with impaired insulin secretion, higher HbA1c (6.1% vs 5.5%), and increased cardiovascular risk markers 2, 3
Clinical Significance of Elevated 1-Hour Values
Risk Stratification
- 1-hour glucose ≥155 mg/dL identifies high-risk individuals even when fasting and 2-hour values remain normal, with these patients showing insulin resistance and beta-cell dysfunction comparable to those with impaired glucose tolerance 2, 3
- 1-hour glucose ≥170 mg/dL predicts mortality in subjects with normal glucose tolerance, with nearly double the death rate from cardiovascular disease and malignancies during 14-year follow-up 5
- Among individuals with normal 2-hour glucose (<140 mg/dL), those with 1-hour values ≥179 mg/dL have 85% sensitivity and 79% specificity for identifying future diabetes risk 4
Cardiovascular Implications
- Elevated 1-hour glucose correlates with increased pulse wave velocity, augmentation pressure, and arterial stiffness in hypertensive patients, independent of fasting or 2-hour values 3
- The 1-hour value shows stronger associations with adverse outcomes than fasting glucose in multiple studies, making it a valuable screening parameter 1, 2
Important Clinical Caveats
The 1-hour measurement is not routinely used for diabetes diagnosis outside of pregnancy - standard diagnostic criteria rely on fasting glucose ≥126 mg/dL or 2-hour glucose ≥200 mg/dL 1
However, measuring 1-hour glucose during OGTT provides additional prognostic information:
- Identifies individuals who would be missed by fasting glucose alone (particularly relevant in Asian populations) 6
- Helps stratify cardiovascular and mortality risk even in those with "normal" glucose tolerance 3, 5
- The Japan Diabetes Society specifically recommends measuring glucose at 30 and 60 minutes during OGTT, noting that 1-hour values >180 mg/dL indicate higher diabetes risk 6
For gestational diabetes, only one elevated value (fasting, 1-hour, or 2-hour) is required for diagnosis using the one-step approach, though the two-step approach requires at least two abnormal values 1, 7