When a person's body is operating normally, it automatically checks the level of glucose in blood. If the level is too high or too low, the body will adjust the sugar level to return it to normal. This system operates in much the same way that cruise control adjusts the speed of a car. With diabetes, the body doesn't do the job of controlling blood glucose automatically. To make up for this, someone with diabetes has to check blood sugar regularly and adjust treatment accordingly.
A doctor can measure blood glucose during an office visit. However, levels change from hour to hour and someone who visits the doctor only every few weeks won't know what his or her blood glucose is daily. Do-it-yourself tests enable people with diabetes to check their blood sugar daily.
The easiest test someone can do at home is a urine test. When the level of glucose in blood rises above normal, the kidneys eliminate the excess glucose in urine. Glucose in urine, therefore, reflects an excess of glucose in blood.
Urine testing is easy. Tablets or paper strips are dipped in urine. The color change that occurs indicates whether blood glucose is too high. However, urine testing is not completely accurate because the reading reflects the level of blood glucose a few hours earlier. In addition, not everyone's kidneys are the same. Even when the amount of glucose in two people's urine is the same, their sugar levels may be different. Certain drugs and vitamin C also can affect the accuracy of urine tests.
It's more accurate to measure blood glucose directly. Kits are available that allow people with diabetes to test their blood glucose at home. The test involves pricking a finger to draw a drop of blood. A spring-operated "lancet" does this automatically. The drop of blood is placed on a strip of specially coated plastic or into a small machine that "reads" how much glucose is in the blood. A doctor may suggest that someone test his or her blood glucose several times a day. Self-blood glucose monitoring can show how the body responds to meals, exercise, stress, and diabetes treatment.
Another test that measures the effectiveness of treatment is a "glycosylated hemoglobin" test. It measures the glucose that has become attached to hemoglobin, the molecule in red blood cells that gives blood its red color. Over time, hemoglobin absorbs glucose, according to its concentration in blood. Once glucose is absorbed by hemoglobin it remains there until the blood cells die and new ones replace them. With the "glycosylated hemoglobin" test, a doctor can tell whether blood glucose has been very high over the last few months.