Follow-up duration influences the relative importance of OGTT and optimal timing of glucose measurements for predicting future type 2 diabetes

Abstract

Objective: To examine the impact of follow-up duration on the incremental prognostic yield of a baseline oral glucose tolerance test (OGTT) for predicting type 2 diabetes and to assess the discrimination ability of blood glucose (BG) obtained at different time points during OGTT. Design: A prospective, population-based cohort study (Malmö Preventive Project) with inclusion of subjects from 1974 to 1992. Methods: A total of 5256 men without diabetes, who had BG measured at 0, 20, 40, 60, 90, and 120 min during OGTT (30 g/m 2 glucose), were followed for 30 years. Incident type 2 diabetes was recorded using registries. The performance of OGTT added to a clinical prediction model (age, body mass index (BMI), diastolic blood pressure, fasting BG, triglycerides, and family history of diabetes) was assessed using Harrell's concordance index (C-index) and integrated discrimination improvement (IDI). Results: Median age was 48 years, mean BMI 24.9 kg/m 2 , and mean fasting BG 4.7 mmol/L. Models with added post-load BG performed better than the clinical model (C-index: P = 0.08 for BG at 120 min at 5 years, otherwise P ≤ 0.045; IDI: P ≥ 0.06 for BG at 60 and 90 min at 5 years, otherwise P ≤ 0.01). With a longer follow-up duration, C-index decreased, and the C-index increase associated with OGTT was attenuated. Models including BG at 60 or 90 min performed significantly better than the model with BG at 120 min, evident beyond follow-up of 10 and 5 years, respectively. Conclusions: OGTT provided incremental prognostic yield for type 2 diabetes prediction. BG measured at 60 or 90 min provided better discrimination than BG at 120 min.

Enhanced Predictive Capability of a 1-Hour Oral Glucose Tolerance Test: A Prospective Population-Based Cohort Study

“…Hence, a more sensitive strategy is needed, which at the same time is simple to use in a primary care setting and less time consuming and more convenient than the 2-h OGTT. The current study extends the results from a previous report from the Malmö Preventive Project and shows that the 1-h time limit provides not only the best compromise in terms of time consumption (performs equivalent to or better than glucose measurement at 90 min) but also prognostic ability (performing better than glucose measurements at 20 and 40 min) (17). The proposed cut point for 1-h blood glucose identifies a substantially larger proportion of subjects at high risk compared with conventional IGT (10,12,13), and its use could lead to more widespread preventive efforts.…”

“…Prior studies have focused mainly on the ability of 1-h glucose measurements to correctly subdivide subjects with NGT into those with low(er) and high(er) risk of future type 2 diabetes and focused less on the direct comparison between 1-h and 2-h OGTT from a clinical standpoint (10,(12)(13)(14)(15). Previous results from the Malmö Preventive Project have further suggested that the 1-h blood glucose level also adds significant predictive value to clinical risk factors (16,17). However, such strategies do not allow for the omission of the 2-h OGTT or preclude the use of complex multivariable clinical prediction models, for which clear cutoff values and benefits upon intervention have not been established.…”

“…Accumulating longitudinal evidence, pioneered in particular by Abdul-Ghani and colleagues (10)(11)(12)(13)(14)(15)(16)(17)(18), suggests that the 1-h postload glucose level during OGTT with a cutoff $8.6 mmol/L (155 mg/dL) may be an early marker of IGT and subsequent type 2 diabetes that is potentially more useful than either fasting or 2-h glucose levels. Furthermore, from a pathophysiological perspective, the 1-h glucose level is intriguing owing to its seemingly strong correlation with markers of both insulin secretion and sensitivity (10,19,20).…”

One-hour and two-hour postload plasma glucose concentrations are comparable predictors of type 2 diabetes mellitus in Southwestern Native Americans

“…The SWNA cohort included young adults with relatively high adiposity at baseline, while other studies included middle-aged adults with relatively low-er adiposity at baseline who also differed with respect to race and ethnicity from our cohort [5, 6, 38], thus emphasising the importance of conducting studies in different populations. The contradictory results may also be explained by different follow-up durations, which have been shown to influence the relative importance of glucose concentrations measured during the OGTT for predicting type 2 diabetes [7]. Group 1 participants also abstained from strenuous exercise and had eaten standardised diets for at least 3 days before the OGTT, representing a procedural difference from the other studies.…”

Use of 1‐h post‐load plasma glucose concentration to identify individuals at high risk of developing Type 2 diabetes

“…The secondary analyses of the Malm€ o Preventive Project and Botnia study found that 1-h PG concentration was superior in predicting Type 2 diabetes; 1-h PG alone was superior to a prediction model consisting of conventional risk factors such as age, sex, BMI and parental history of diabetes [5]. Furthermore, 1-h PG performed significantly better than 2-h PG over 30 years [6].…”