Hi in 2010 American Diabetic Association guidelines allowed HBa1c for diagnosis of diabetes. However unless there is "unequivocal hyperglycaemia" then repeat testing is needed. This link clarifies the same test is recommended. The interval between tests is unclear but some sources say as soon as possible. However I cannot find any evidence from any proimary study looking at the validity of this protocol (esp repeat hba1c testing)/. Surely a repeat hba1c is very likely to show the same result unless done with an interval of weeks?

thank you

http://care.diabetesjournals.org/content/39/Supplement_1/S13

"Confirming the Diagnosis Unless there is a clear clinical diagnosis (e.g., patient in a hyperglycemic crisis or with classic symptoms of hyperglycemia and a random plasma glucose ≥200 mg/dL [11.1 mmol/L]), a second test is required for confirmation. It is recommended that the same test be repeated without delay using a new blood sample for confirmation because there will be a greater likelihood of concurrence. For example, if the A1C is 7.0% (53 mmol/mol) and a repeat result is 6.8% (51 mmol/mol), the diagnosis of diabetes is confirmed. If two different tests (such as A1C and FPG) are both above the diagnostic threshold, this also confirms the diagnosis. On the other hand, if a patient has discordant results from two different tests, then the test result that is above the diagnostic cut point should be repeated. The diagnosis is made on the basis of the confirmed test. For example, if a patient meets the diabetes criterion of the A1C (two results ≥6.5% [48 mmol/mol]) but not FPG (