Diabetes Glucose in Urine
A normal person usually does not pass glucose in the urine Glucose appears in urine when the blood glucose level exceeds about 180 mg/dl. This limit is called renal or kidney threshold for glucose. The kidney threshold for glucose may vary from person to person or in the same person from time to time. In some persons this threshold may be low. They pass glucose in urine even when their blood glucose level is normal. Such persons are often stamped diabetic without justification and subjected to unnecessary restrictions. The kidney threshold is reduced during pregnancy. In children, the threshold is often low. Some drugs may alter the kidney threshold.
On the other hand, in some diabetics, for instance, the elderly, those with a long standing disease and those with an impaired kidney function, the kidney threshold for glucose may be very high. In such persons, urine may be free from glucose although the blood glucose level is high. The absence of glucose in urine makes people complacent and believe that their diabetes is well controlled or even cured!
The knowledge of the kidney threshold for glucose is essential for interpretation of the results of urine glucose tests. Simultaneous blood glucose and urine glucose tests give an idea of the kidney threshold for glucose.
A negative urine glucose test does not necessarily mean that the blood glucose level is normal. Blood glucose level may be anywhere between 0 to 160 mg/dl, with a negative urine glucose test. Hence, one cannot differentiate, on basis of a negative urine glucose test, between low, normal or a mildly elevated blood glucose level.
Urine glucose depends on fluid balance and urine concentration. It must be remembered that the urine glucose value does not reflect the blood glucose value at that particular moment but reflects values few hours prior to the urine collection.
Methods for testing for Glucose
PAPER STRIP TEST
This test consists of a strip of paper, one end of which is impregnated with an enzyme that oxidizes glucose and a coloring system.
Material: The complete kit is supplied by the manufacturer.
Method: Dip the reagent end of the strip for 1-2 seconds in the urine and remove. Gently tap the strip on the side of the urine container to remove excess of urine. Wait for a specified time after removing the excess urine. Match the color of the reagent end of the strip with the chart provided and find out the urine glucose percentage. The paper strip test is specific for glucose. A false negative result for example, may be obtained if the person is taking vitamin C, salicylates (pain relieving drug, aspirin) or levodopa (a drug given for Parkinsonism).
The test, though convenient, is expensive. The test strips have a short shelf line and deteriorate with exposure to air and moisture.
These paper strips only tell whether glucose is present in urine or not.
Urine tests for Glucose - Common Errors
| Material | : Outdated material: paper stripsdeteriorated by heat, sunlight, moisture; unstoppered bottle of paper strips. |
| Technique | : Wrong waiting period. |
| Lighting | : Inadequate |
| Vision | : Poor vision, especially for colors. |
Record of urine test
The results of urine lest should be recorded systematically in a book as shown below.
Urine test method*
Date Time Dose of insulin and/or oral drugs
Glucose per cent * Noting color without specifying the method employed can be very misleading.
Fasting urine sample
The urine passed first time in the morning is not the fasting sample since this urine was produced at night and collected in the urinary bladder. To collect fasting sample, urine passed first in the morning (first void) is discarded. Urine passed again after half an hour (second void) without eating anything is the fasting sample.
Importance of urine glucose tests
An examination of urine for glucose is often an important initial step in the diagnosis of diabetes. Often, diabetes is suspected for the first time when glucose is detected in a routine examination of urine.
Urine glucose testing should be done by those diabetic individuals who are unwilling to do blood glucose testing or cannot afford the same.