Although urine glucose monitoring has been used in the past for people with diabetes to monitor their glucose (sugar) levels, it has now largely been replaced by blood glucose monitoring using a personal blood glucose meter. However, urine glucose tests may occasionally be done in some circumstances to give a rough indication of high glucose levels.
What does urine glucose testing measure?
A urine glucose test can tell you whether there is glucose (sugar) in the urine, and gives an indication of the glucose level. If glucose is found in your urine it is called glycosuria or glucosuria.
Glucose is usually only found in the urine when blood glucose levels are raised due to diabetes. When your blood glucose levels are high enough, glycosuria occurs because your kidneys can’t stop glucose from spilling over from the bloodstream into the urine. In most people, blood glucose levels above 10 mmol of glucose per litre of plasma will cause glucose to appear in the urine. This level is called the ‘renal threshold’ for glucose.
Glucose in the urine can sometimes occur as a side effect of certain medicines and in people with certain kidney problems, including a rare condition called renal glycosuria, where glucose is found in the urine despite normal blood glucose levels.
What does urine glucose testing involve?
If you sometimes check your diabetes with urine glucose testing, you will be advised which time of day to perform the test. Make sure you understand how to perform the test, and go over the instructions for your brand of test strip with your doctor or diabetes educator.
To perform the test:
- collect a small amount of urine;
- expose the test strip or dipstick to the urine, usually by dipping it in the urine sample;
- read the test result at the specified time, by comparing the colour change on the test strip with the reference colour chart, which is usually printed on the container.
It’s a good idea to write down your test results or keep a chart of them, and take these with you when you see your doctor or diabetes educator. Also note down any special circumstances at the time of the test, for example, if you were unwell, were under emotional stress, had changed the amount or type of food you were eating or were taking medicine to treat another condition.
Limitations of urine glucose monitoring
Monitoring diabetes control by testing urine glucose levels is rarely recommended, due to the limitations of this method. These limitations include the following.
- Urine glucose tests do not reflect your blood glucose level at the time of testing; instead, they only give an indication of blood glucose levels over the previous several hours. For example, some of the urine present in your bladder may be 2 hours old, and may show glucose even though your blood glucose level may have normalised since then. Compare this to a blood glucose test which gives you a reading of your blood glucose level at that moment.
- Urine glucose tests do not give you any information about low blood glucose levels, as glucose only ‘overflows’ into the urine when the blood glucose level gets above about 10 mmol/L. So, a negative urine glucose test may be the result of a normal blood glucose level or a dangerously low blood glucose level (hypoglycaemia), with the urine glucose test unable to differentiate between the 2 situations.
- The results of urine glucose tests are influenced by the volume and concentration of urine that you pass, which will vary with the amount of fluid you consume and your fluid loss due to such things as heavy sweating or vomiting.
- Urine glucose tests that are designed for home use rely on interpreting a colour change to define the result. Subtle colour differences may be difficult to interpret.
- If a urine glucose test is not read at the specified time after exposing the test strip to the urine, then the result is prone to error.
- Some medications may interfere with the results of urine glucose testing.
Advantages of urine glucose monitoring
There are a couple of advantages of urine glucose monitoring.
- It is less painful than blood glucose monitoring — no finger pricks to collect blood samples for testing.
- Urine test strips may be less costly than buying a blood glucose monitor and its test strips.