There are three ways to diagnose preexisting diabetes mellitus and each way must be confirmed by a follow-up test. Criteria for diagnosing diabetes mellitus include:
(1) Symptoms of diabetes (polyuria, polydipsia, and/or unexplained weight loss) plus a casual plasma glucose concentration of equal to or greater than 200 mg/dL,
(2) Fasting plasma glucose (at least 8 hours without eating) equal to or greater than 126 mg/dL,
(3) Two-hour plasma glucose of equal to or greater than 200 mg/dL after drinking a 75-gram glucose load.
A positive value on any of these tests should be confirmed on a subsequent day by repeating any of these tests.