Diabetic Home Care and Monitoring (cont.)
Urine glucose tests
The role for home urine glucose testing has faded with the easy use of fingerstick blood glucose monitoring. For those few patients who choose to do home urine glucose testing, they need to realize the limitations. It is only a rough estimate of blood glucose values.
Also, it provides no information unless the kidney is spilling glucose, and that usually occurs at a blood glucose level of greater than 180mg/dl. Below that, the urine glucose values are negative.
Urine glucose levels should not be confused with checking microalbumin levels and protein levels. These tests are performed in the doctor's office at least on an annual basis, and provide necessary information about kidney function, and provide the basis for obtaining information to see whether certain medications should be added.
Urine 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, but blood levels of glucose
still may be unacceptably high. 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.
The tests uses 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, which is 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 and lead to false positive
results, meaning the test 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.
Next: Tests for urinary ketones »
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