What Is the Difference Between Urine Glucose and Blood Glucose?

Glucose is a simple sugar that exists in many types of food and in your blood. It serves many functions, the most important of which is as an energy source. Your body has sensitive systems for keeping the glucose in your blood within a normal range. However, in conditions such as diabetes, blood glucose levels can become elevated, causing glucose to spill out into your urine. In pregnancy, glucose may appear in the urine, although the blood glucose level is typically normal.

Glucose is a simple carbohydrate, and many dietary sources exist. In fact, glucose is present in nearly all foods that contain carbohydrates. Glucose can be present on its own, or paired with fructose to form the two-sugar molecule sucrose, also known as table sugar. Other sources of glucose include fruits and vegetables. Grains, legumes, nuts and seeds contain large molecules of glucose known as starch. Sweeteners such as maple syrup, honey, high-fructose corn syrup and molasses also contain abundant quantities of glucose. Animal products such as fish, being carbohydrate-free, do not contain glucose.

The major function of glucose is to provide energy to your cells. Once it is broken down in your small intestine, it is absorbed into the bloodstream, where it travels throughout your body and can enter the cells of every major organ. Within your cells, glucose undergoes chemical reactions called glycolysis and the Krebs Cycle, in which it is broken down and combined with oxygen to produce ATP, the energy currency of your body. ATP, or adenosine triphosphate, helps your body undergo chemical reactions such as building new proteins and recycling old cells.

The normal range for blood glucose is from 70 to 115 mg/dL, according to "Maxwell Quick Medical Reference." To keep the glucose you consume within this range, your pancreas secretes the hormone insulin, which drives glucose into your cells, where it can be used for fuel. In diabetes, the pancreas is unable to secrete insulin either at all or in sufficient quantities to meet your body's requirement. As a result, glucose remains in the blood, where levels can rise to over 1000 mg/dL, or 10 times the upper limit of normal. When this happens, some of the glucose present in the blood enters the urine.

Urine glucose, also known as glycosuria, is usually caused by uncontrolled diabetes. Healthy individuals are able to maintain blood glucose within normal range and so no excess appears in the urine. Exceptions exist, however. Nondiabetic glycosuria, also known as renal glycosuria, is a benign condition in which glucose appears in the urine despite normal blood levels. There are no symptoms associated with this condition, which occurs in as many as 50 percent of pregnancies, especially in the third and fourth months, according to "Current Medical Diagnosis and Treatment, 2011." No treatment is necessary, and glucose generally disappears from the urine after delivery.