Diabetic Home Care and Monitoring (cont.)

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Urine glucose tests

The role for testing urinary glucose at home has faded with universal blood glucose monitoring by fingerstick. Those few patients who choose to test urinary glucose must realize its limitations. Urinary glucose only estimates blood glucose values roughly, and it provides no information at all unless there is glucose in the urine. Glucose appears in the urine when the blood glucose level is over 180 mg/dL, well above the target for most patients. Below that level, urinary glucose is usually negative.

Urinary glucose levels should not be confused with checking urinary microalbumin and related protein levels. Urinary glucose levels should not be confused with checking urinary microalbumin and related protein levels. Performed in the doctor's office at least annually, these tests provide necessary information about kidney function the basis for determining whether certain medications should be added to the treatment plan to protect kidney function.

Urinary glucose tests also do not indicate the current blood glucose level, but rather the glucose level during the period of time between the collection of the urine and the previous urination. In many patients, the level of blood glucose must be very high in order for glucose to appear in the urine. Therefore, the urine may be free of glucose, despite unacceptably high blood levels of glucose. Thus, results from urine glucose tests should not be used to adjust insulin doses.

There are two types of urine glucose tests. Both types rely on a chemical reaction that produces a color change. These tests use either tablets or strips. Generally, the test strip or tablet is placed in urine. The resulting color change is matched against a color chart provided by the manufacturer, which shows the different colors produced by different levels of glucose.

The first type, called the copper reduction test, uses cupric sulfate (for example, Clinitest). In the presence of glucose, cupric sulfate (which is blue) changes to cuprous oxide (green to orange). The reaction should be observed closely and the manufacturer's instructions closely followed. The copper reduction tests can react with substances other than glucose in the urine, leading to false positive results. This means the test erroneously shows glucose when it is not present. Examples of these other substances include aspirin, penicillin, isoniazid (Nydrazid, Laniazid), vitamin C, and cephalosporin-type antibiotics. Tablets and solutions utilizing copper reduction may damage the skin and are poisonous if ingested. They should be handled carefully and kept out of the reach of children.

The second type of urine glucose test, called the glucose oxidase test, uses the chemical toluidine and the enzyme glucose oxidase (for example, Clinistix). Glucose oxidase converts the glucose in urine to gluconic acid and hydrogen peroxide. The interaction of the hydrogen peroxide with the toluidine causes a change in color. False negative results (meaning the test shows no glucose when glucose really is present) may occur in patients taking vitamin C, aspirin, iron supplements, levodopa (Sinemet), and tetracycline-type antibiotics. Glucose oxidase tests are more convenient to use and less expensive than copper reduction tests. The strips should be kept away from moisture.

Medically Reviewed by a Doctor on 12/4/2014

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