At the recent American Diabetes Association 78th Scientific Sessions (held June 7-11), several presentations focusing on diabetes and prediabetes prevention revealed clinically important findings, which I will discuss below.
The 1-hour plasma glucose (1-h-PG) > 155 mg/dl during an oral glucose tolerance test (OGTT) in individuals with normal fasting and 2-hour plasma glucose (2h-PG) values have been shown to be a more sensitive predictor for prediabetes and type 2 diabetes (T2D). The 1-hr PG has a greater capacity for detecting micro- and macrovascular complications and mortality than HbA1c, the fasting plasma, or 2-hour plasma glucose levels.
Two important questions that need to be addressed:
- Whether the 1-hr PG > 155 mg/dl represents a different phenotypic pattern than the 2-hr PG > 140 mg/dl defining impaired glucose tolerance (IGT) or whether the 1-hr PG antecedes progression to IGT en route to eventual T2D;
- The 1h-PG that correlates with the 2h-PG level diagnostic of T2D (> 200 mg/dl). A poster entitled “Using Longitudinal Modeling to Find One-hour Glucose Alternatives to Two-Hour Glucose for Prediction and Diagnosis of Glucose Tolerance” was presented for a moderated discussion at ADA [Diabetes 2019 Jun;68 (Supplement 1):https//doi.org/10.2337/db19-1490-P]. Joon Ha, PhD and colleagues used a longitudinal mathematical model to predict the pattern of glucose rise in the 1h-PG and 2h-PG concentrations with time and tested these predictions in a longitudinal cohort of 52 Pima Indians (baseline age, 26.5±5.8 years; BMI, 36.6±5.8 kg/m2) who were followed for 7.2±3.5 years. Model simulations suggested that the 1h-PG would pass the threshold of 155 mg/dl before the 2h-PG passed the IGT threshold of 140 mg/dl in most individuals. Participants had a median of 6 (range 3 – 11) separate OGTTs, 1.7±0.8 years apart. A 1h-PG of 155 mg/dl was observed 1.9±2.0 years before the 2h-PG reached the IGT threshold (> 140 mg/dl).
Overall, the times of crossing the 1h-PG threshold of 155 mg/dl and the 2h-PG IGT threshold correlated, but as the 1h-PG crossed earlier, this provided an earlier indication of future hyperglycemia. Furthermore, the average 1h-PG value of 217 mg/dl occurred when the 2h-PG level reached the threshold value of 200 mg/dl, diagnostic of T2D. Additionally, since 1h-PG and 2h-PG rise together during the progression from prediabetes to T2DM, a 1h-PG of 217 mg/dl could be an alternative marker to the 2h-PG of 200 mg/dl for the diagnosis of T2D.
These observations have potentially important clinical implications:
(1) As the 1-hr PG > 155 mg/dl occurs before IGT (2-hr PG > 140 mg/dl), prescribing intensive lifestyle modification when the 1-hr PG level is elevated could be even more effective for reducing progression to T2D than what has been previously demonstrated during the Diabetes Prevention Program in individuals with IGT, as β-cell function is likely to be better preserved.
(2) The elevated 1h-PG glucose could potentially replace the 2-hr OGTT for detecting both prediabetes with the threshold value > 155 mg/dl and diagnosing T2D when the 1h-PG exceeds 217 mg/dl. If confirmed in further studies, the implications would be considerable as the OGTT could then be abbreviated to 1-hr making it more acceptable in clinical practice.
Michael Bergman, MD is an endocrinologist. He is a clinical professor of medicine and population health at the New York University School of Medicine, Director of the NYU Diabetes Prevention Program and Section Chief of Endocrinology, Diabetes, Metabolism at the Manhattan VA.
Illustration by Jennifer Bogartz