To examine the prevalence and person-level predictors of undiagnosed Type 2 diabetes among adults with elevated HbA1c values. We identified adults without diabetes who had a first elevated HbA1c (index HbA1c ≥ 48 mmol/mol; ≥ 6.5%) between January 2014 and December 2015, and classified them by Type 2 diabetes diagnosis status at 1 year following this result. Multilevel modelling techniques were used to examine the association of individual demographic, clinical, and utilization characteristics with remaining undiagnosed. We quantified differences in early Type 2 diabetes care between diagnosed and undiagnosed individuals. Of the 18 356 adults with a first elevated index HbA1c , 30.2% remained undiagnosed with Type 2 diabetes 1 year later. Individuals with lower index HbA1c values [adjusted odds ratio (aOR) 5.95, 95% confidence interval (CI) 5.21-6.78 for 48 to <53 mmol/mol (6.5% to 7.0%); referent 53 to <64 mmol/mol (7.0% to <8.0%)], who were ≥ 70 years old (aOR 1.40, 95% CI 1.24-1.59; referent 50-59 years), and who had a prior prediabetes diagnosis (aOR 1.35, 95% CI 1.24-1.47; referent no prediabetes) had increased odds of remaining undiagnosed. After adjusting for age, race, and index HbA1c , remaining undiagnosed was associated with lower odds of initiating metformin (aOR 0.06, 95% CI 0.05-0.07). Almost one-third of adults with an elevated HbA1c value were not diagnosed with Type 2 diabetes within 1 year. Undiagnosed Type 2 diabetes, in turn, was associated with differences in early care. Strategies that leverage the electronic health record to facilitate earlier diagnosis may help reduce delays and allow for early intervention towards the goal of improved outcomes.