['Serum α-hydroxybutyrate (α-HB) is elevated in insulin resistance and diabetes. We tested the hypothesis that the α-HB level predicts abnormal 1\u2005h glucose levels and β-cell dysfunction inferred from plasma insulin kinetics during a 75\u2005g oral glucose tolerance test (OGTT).', 'This cross-sectional study included 217 patients at increased risk for diabetes. 75\u2005g OGTTs were performed with multiple postload glucose and insulin measurements over a 30-120\u2005min period. OGTT responses were analyzed by repeated measures analysis of variance (ANOVA). Multivariable logistic regression was used to predict 1\u2005h glucose ≥155\u2005mg/dL with α-HB added to traditional risk factors.', 'Mean±SD age was 51±15\u2005years (44% male, 25% with impaired glucose tolerance). Fasting glucose and insulin levels, but not age or body mass index (BMI), were significantly higher in the second/third α-HB tertiles (>3.9\u2005µg/mL) than in the first tertile. Patients in the second/third α-HB tertiles exhibited a higher glucose area under the receiver operating characteristics curve (AUC) and reduced initial slope of insulin response during OGTT. The AUC for predicting 1\u2005h glucose ≥155\u2005mg/dL was 0.82 for a base model that included age, gender, BMI, fasting glucose, glycated hemoglobin (HbA1c), and insulin, and increased to 0.86 with α-HB added (p=0.015), with a net reclassification index of 52% (p<0.0001).'] Does serum α-hydroxybutyrate ( α-HB ) predict elevated 1 h glucose levels and early-phase β-cell dysfunction during OGTT?