Abstract Aims To examine the ability of fasting plasma glucose (FPG) and/or 2-h glucose to confirm diabetes and to determine the proportion of participants with HbA1c ≥6.5%. Methods Diabetes confirmation rates were calculated after a single elevated FPG and/or 2-h glucose on an oral glucose tolerance test (OGTT) using a confirmatory OGTT performed within 6weeks. Results 772 (24%) participants had elevated FPG or 2-h glucose on an OGTT that triggered a confirmation visit. There were 101 triggers on FPG alone, 574 on 2-h glucose alone, and 97 on both. Only 47% of participants who triggered had confirmed diabetes. While the confirmation rate for FPG was higher than that for 2-h glucose, the larger number of 2-h glucose triggers resulted in 87% of confirmed cases triggering on 2-h glucose. Confirmation rates increased to 75% among persons with FPG ≥126mg/dl and HbA1c ≥6.5%. Conclusions Only half of the persons with elevated FPG and IGT were subsequently confirmed to have diabetes. At current diagnostic levels, more persons trigger on 2-h glucose than on FPG, but fewer of these persons have their diagnoses confirmed. In individuals with FPG ≥126mg/dl and HbA1c ≥6.5%, the confirmation rate was increased.