Test for glycosuria, the excretion of glucose in the urine. The test for urine glucose uses a small dipstick that changes color after it has been dipped in urine. Matching the color on the dipstick against a chart on the test package reveals whether there is glucose in the urine.
Before people with diabetes started measuring blood glucose levels, urine glucose testing was the best way to monitor diabetes control. Some people still use urine glucose tests, but these tests are of dubious value in monitoring diabetes control for two reasons.
First, the renal threshold—the blood glucose level at which the kidneys begin to excrete glucose in the urine—is relatively high. In healthy, nondiabetic individuals, the average renal threshold is at a blood glucose level of 160–180 mg/dl. In other words, only when the blood glucose level reaches 160–180 mg/dl will some glucose appear in the urine. Many people with diabetes have an even higher renal threshold, so glucose will not appear in their urine until blood glucose levels are very high—well above the normal range. Thus, a positive urine glucose test would indicate that the blood glucose level is very high, and a negative urine glucose test could mean that the level is low, normal, or slightly elevated.
The second factor that limits the value of this test is that urine can remain in the bladder for several hours, which means that a positive urine glucose test may actually reflect a high blood glucose level from several hours ago, even if the current blood glucose level is actually normal.