In this study, we show that both the 1-h PG during an OGTT and CGM-derived GV indices identify individuals with dysglycemia despite having normal HbA1c. In addition, both PG and CGM during an OGTT can detect early β-cell dysfunction, that is not captured by HbA1c.
We demonstrate that PG and CGM glucose levels correlate during an OGTT and that the 1-h PG highly correlated with GV indices. Thus, either the 1-h PG or CGM interstitial glucose during an OGTT provide information regarding GV. Consistent with previous findings, subjects with a 1-h high PG level had higher GV indices which included MAGE, SD, and LI, compared to those with 1-h low levels . Moreover, 1-h PG ≥ 155 mg/dL (8.6 mmol/L) during an OGTT is a sensitive predictor for future development of diabetes, cardiovascular risk, and mortality [4, 11, 12].
Previous studies have found that 1-h PG outperforms HbA1c, and 2-h PG in detecting dysglycemia [13, 14]. Our findings further demonstrate that the 1-h PG tracks with GV indices, thus CGM-derived GV indices can be used to identify early β-cell dysfunction. A previous study showed that both SD and MAGE were increased in patients with prediabetes identified by OGTT compared to those with normal glucose tolerance . Our study adds the important observation that high-risk individuals with HbA1c < 5.7% (39 mmol/mol) can have increased GV. CGM can further analyze daily and time-related glycemic patterns that may provide valuable feedback and educate patients regarding benefits derived from improved food choices and exercise. CGMs therefore add information beyond the diagnostic information obtained with a 1-h PG alone.
Although all subjects had a HbA1c < 5.7% (39 mmol/mol), 53% of subjects had 1-h PG ≥ 155 mg/dL (8.6 mmol/L). Once the HbA1c is in the prediabetes range (5.7–6.4% [39–46 mmol/mol]), β-cell dysfunction may already have reached an advanced stage, making reversibility less likely. Early identification of dysglycemia is therefore paramount. These findings underscore that a normal HbA1c underestimates the prevalence of individuals with dysglycemia or early β-cell dysfunction. Therefore, detecting GV using either 1-h PG or CGM interstitial glucose values appears to be more sensitive than the HbA1c in screening high-risk individuals . We have demonstrated that CGM is also useful in screening for dysglycemia in subjects with normal HbA1c since it captures considerable glucose determinations up to 2 weeks in a “free-living” environment. A limitation to our study is that it took place during the COVID-19 pandemic which restricted recruitment. Nonetheless, our study shows that 1-h PG and 1-h CGM interstitial glucose are useful for identifying GV and dysglycemia in individuals with normal HbA1c but at high-risk for type 2 diabetes. Moreover, CGM can identify dysglycemia and may be a potential alternative to PG determinations during an OGTT. Future studies should recruit a larger, more diverse cohort to show the utility of the CGM in predicting early dysglycemia in a broader population.