What lab test is used to diagnose diabetes mellitus?

The fasting blood glucose test and the oral glucose tolerance test (OGTT) are key diagnostic tools for diabetes mellitus. The fasting blood glucose test measures the blood sugar levels after the patient has not eaten for at least eight hours. A result of 126 mg/dL or higher indicates diabetes. The OGTT involves fasting and then drinking a glucose-rich beverage, with blood sugar levels tested at intervals afterward. A two-hour blood glucose level of 200 mg/dL or higher also signifies diabetes.

These tests are fundamental in diagnosing diabetes because they directly assess how well the body manages glucose, which is critical in the condition. While the hemoglobin A1C test is also a valid diagnostic tool as it provides an average blood glucose level over the past two to three months, the fasting blood glucose and OGTT are often used for initial diagnosis due to their direct nature regarding acute glucose management.

The complete blood count and lipid profile do not provide specific information about glucose levels and, thus, are not utilized for diagnosing diabetes mellitus.