Glucose is a simple sugar and the primary source of energy for cells in the human body. The majority of food in the digestive system ends up being broken down into glucose by various enzymes and other chemicals. People with diabetes or other disorders can have trouble creating the glucose or using it correctly, however. A serum glucose test allows patients to determine whether they have any digestive or metabolism disorders.

Doctors usually recommend a serum glucose test when screening for diabetes or related problems such as prediabetes. This kind of test can also help determine whether a person has high blood glucose, or hyperglycemia, which can cause organ damage if it goes untreated. Hypoglycemia, or low blood sugar, can also be detected by this test. Patients who already have diabetes may use a serum glucose test to check the effectiveness of their treatment plans

Most diagnostic tests are fasting glucose tests, performed to determine the blood sugar level when there is no new food in the system. Normal readings range from 70 to 99 milligrams per deciliter, while prediabetic people tend to show readings between 100 and 125 mh/dL. If a patient shows readings of 126 mg/dL or greater on more than one testing occasion, this indicates diabetes. It's important for patients not to eat or drink anything for 10 hours before the test, avoid extreme stress and to tell technicians if they are using diuretics, estrogen therapy, birth control pills, tricyclics, corticosteroids, lithium or any other medications that can artificially raise or lower blood glucose levels.