CUT-OFF POINT FOR FASTING GLUCOSE IN DIAGNOSING PREDIABETES

Objective. This study aimed to evaluate the feasibility of using fasting glucose as a primary diagnostic criterion for prediabetes, and to determine the optimal cut-off point for differentiating between normal glucose metabolism and impaired glucose metabolism (including both prediabetes and diabetes mellitus) based on fasting glucose levels. Participants and Methods. A total of 134 individuals (32 men and 102 women), aged 20 to 79 years, were enrolled in the study. All participants underwent anthropometric assessment and laboratory evaluation. A 75 g oral glucose tolerance test (OGTT) was performed, with venous plasma glucose measurements obtained at 30, 60, 90, and 120 minutes post-glucose load. Glycated hemoglobin (HbA1c) levels were measured using the SDA1c Care analyzer (SD Biosensor, Korea). Fasting and post-load plasma glucose concentrations were determined using the Precision PCx MediSense system (Abbott, USA). To identify predictive factors for fasting glucose, linear and multiple regression analyses were conducted. These regression models were subsequently used to estimate fasting glucose levels. Qualitative diagnostic parameters (e.g., sensitivity, specificity, Youden Index) were applied to determine the optimal cut-off point for fasting glucose in distinguishing between normal and impaired glucose metabolism. Results. The standardization of diagnostic criteria for prediabetes remains a subject of ongoing debate. While the boundary between prediabetes and diabetes is widely accepted, and the upper and lower thresholds of prediabetes are commonly defined based on plasma glucose levels 120 minutes after a 75 g glucose load (GL120), consensus regarding fasting glucose criteria is less established. This study was based on the identification of statistically significant correlations between: fasting glucose and GL120 (r = +0.61, 95% CI [+0.492, +0.706], p < 0.0001); fasting glucose and HbA1c (r = +0.63, 95% CI [+0.516, +0.722], p < 0.0001). Using regression analysis, multiple predictive equations were constructed to estimate fasting glucose levels. Subsequently, the diagnostic quality characteristics (sensitivity, specificity, Youden Index, AUC) for the calculated and other potential fasting glucose cut-off points were evaluated. The Youden Index for cut-off point≥100 mg/dl mg/dl was 60.3 %; maximal Youden Index for fasting glucose cut-off point ≥110 mg/dl was 70.2 %. We obtained a finding of 0.80 for the AUC, indicating good discriminative ability. Conclusion. The fasting glucose cut-off point of ≥110 mg/dL demonstrates favorable diagnostic performance for the detection of prediabetes. With a Youden Index of 70.2% and an AUC of 0.80, this threshold offers a strong balance of sensitivity and specificity. These results support the use of the ≥110 mg/dL fasting glucose level as a practical and evidence-based criterion for identifying individuals at risk for prediabetes.