What diagnostic criterion is used to confirm diabetes mellitus?

The criterion for diagnosing diabetes mellitus is an 8-hour fasting blood glucose level of 126 mg/dL or higher. This measurement is critical because it reflects the body's ability to regulate blood sugar levels properly after a period without food intake.

When blood glucose levels reach or exceed 126 mg/dL, it indicates that the body is not adequately producing or responding to insulin, leading to sustained high levels of glucose in the bloodstream. This threshold has been established by health organizations such as the American Diabetes Association as a key diagnostic marker for diabetes.

Other thresholds, such as a fasting blood glucose of less than 100 mg/dL, indicate normal glucose metabolism, while a random blood glucose of 150 mg/dL alone does not provide sufficient context to diagnose diabetes without other corroborating information. An oral glucose tolerance test that results in a level of 120 mg/dL falls within the range of normal and does not meet the criteria for diagnosing diabetes either.