The diagnosis of Diabetes Mellitus depends on the measurement of blood glucose levels. Blood glucose fluctuates in response to ingestion of food. Blood glucose will be higher 1 to 2 hours after a meal than it will be 8 to 10 hours after a meal. Based on extensive studies, normal ranges for blood glucose levels have been established. Blood glucose levels which exceed these ranges are abnormal and said to be elevated. The risk for Diabetes Mellitus increases the further the blood glucose elevation falls outside of the normal range.

A fasting blood glucose is the most commonly used screen for Diabetes Mellitus. It measures blood glucose after a set period of time since the last ingestion of food. Occasionally, an oral glucose tolerance test is also necessary. This measures glucose levels at timed intervals over a 3-hour period following the ingestion of a prescribed amount of glucose.

Once blood glucose reaches levels of 180 or higher, glucose can be detected in the urine. However, some persons will spill glucose in their urine even when blood glucose levels are within normal limits. The finding of glucose in the urine should be evaluated with a blood glucose measurement.

Northwestern Mutual utilizes a blood glucose and fructosamine as initial screens for Diabetes Mellitus. Depending on the value of the blood glucose and/or fructosamine, a hemoglobin A1C may also be measured. Hemoglobin A1C reflects a person's average blood glucose level for the preceding 2 to 3 months. Fructosamine measures the average glucose level for the preceding 2 to 3 weeks. Diabetes Mellitus cannot be diagnosed on the basis of one set of abnormal tests. Abnormal results are best interpreted by a person's personal physician.