Which laboratory test can determine whether Rita has diabetes mellitus?

The fasting blood glucose test is a reliable method for determining whether an individual has diabetes mellitus. This test measures the blood sugar level after an overnight fast, providing a snapshot of how well the body regulates glucose when no food has been consumed. A fasting blood glucose level of 126 mg/dL (7.0 mmol/L) or higher indicates a diagnosis of diabetes.

Additional tests, such as the oral glucose tolerance test, hemoglobin A1C test, and random blood sugar test, also play crucial roles in diabetes diagnosis. The oral glucose tolerance test evaluates the body's ability to handle a specified glucose load over time, while the hemoglobin A1C test provides an average blood sugar level over the previous three months. A random blood sugar test measures glucose at any time, which can be useful, but it is not solely definitive for diagnosing diabetes unless accompanied by signs or symptoms.

Therefore, the fasting blood glucose test is particularly valued for its simplicity and effectiveness in establishing a baseline of glucose regulation, making it a key option for diabetes diagnosis.