In a healthy individual, most of the food eaten is broken down into glucose and other simple sugars. Glucose is absorbed into the blood and later used by cells for energy. As glucose levels rise following eating, the pancreas releases insulin. The insulin attaches to cell receptor sites, ''opening'' the cells for the glucose to enter. When the pancreas does not produce enough insulin to open the cells, glucose builds up in the blood, leading to hyperglycemia or high blood sugar.
Excess glucose passes through the kidneys, causing frequent urination and increased thirst.
Diagnosing Diabetes Diabetes is diagnosed based on above-normal levels of glucose in the blood. There are different blood tests used to diagnose diabetes and the results from one test cannot be compared with those from another. This test is used to determine the plasma glucose concentration in the fasting state. This test studies the plasma glucose concentration any time. No fasting is required.