The New Straits Times, May 8, 1998
Q: My mother has Type II diabetes and is on a drug called glibenclamide to control her blood glucose. She is reluctant to test her blood glucose concentration but is willing to do the urine glucose test. Can you describe the advantages and disadvantages of urine glucose tests relative to home blood glucose monitoring?
A: The goal of therapy in this case usually involves improving the blood glucose level to within a certain level, depending on whether the patient has consumed food or not. For this, the ideal level of blood glucose under the fasting state is 115mg/100ml; if the patient has consumed food, the blood glucose should be below 180mg/100ml. Thus, the monitoring of blood glucose is an important component in the management of diabetes.
Blood glucose monitoring has enabled patients and their physicians to directly assess the effect of drug doses, dietary patterns, exercise and illness on blood glucose concentrations. Ideally, home blood glucose monitoring can provide an accurate profile of the blood glucose, and provide a convenient mode of testing that can be incorporated into the daily routine of diabetic patients. However, they are expensive, invasive and very technique-dependent.
Furthermore, to achieve maximum benefits with this monitoring, both the clinician and patient must be motivated and willing to spend time understanding its use in achieving normal blood glucose control. For the patient, the practice of home blood glucose monitoring can bring maximum benefits for the treatment of diabetes in the following groups:
Unstable Type 1 diabetic patients
Blood glucose provides the unstable insulin-dependent diabetic patient with several benefits. Instant feedback provides an increased sense of control and motivation and frequent blood glucose measurements help the patient correlate diet, exercise, and insulin dose with blood glucose concentrations. Most importantly, this monitoring can improve control in unstable patients.
Pregnant diabetic patients
Infant morbidity and mortality may be associated with the mother's overall glucose control. With the home blood glucose monitoring, the diabetic mother who achieves tight control improves her chances of delivering a healthy, infant.
Patients with difficulty recognising low glucose level
Acute anxiety attacks or signs and symptoms associated with a rapidly falling blood glucose concentration may mimic a true low level glucose reaction. This can be easily evaluated by measuring blood glucose concentration.
Patients with an abnormal or unstable renal threshold
Although the average renal threshold for glucose is approximately 180mg/dL, the threshold varies greatly among individuals. Blood glucose is normally used in the patients with high renal thresholds or in those with urinary retention.
Patients who are on intensive insulin therapy
Individuals who are on multiple daily doses of insulin or those using an insulin pump should practise home blood glucose monitoring to evaluate the adequacy of their insulin regimen and to check for hypoglycemic reactions.
Impaired colour vision
Many colour-blind patients who are unable to visually read urine and/or blood glucose strips are able to read the digital reading provided by certain blood glucose instruments.
When the patient is reluctant to carry out a blood glucose test although it provides a more accurate profile of the blood glucose, the alternative is to perform the urine glucose test. Initially, urine glucose tests were the primary tools for monitoring diabetic control. The main advantage of the urine glucose method is that it is inexpensive, painless and non-invasive.
Urine glucose tests are only positive when blood glucose concentrations exceed the renal threshold (180mg/dL). Therefore, a negative test may reflect a blood glucose concentration which ranges from zero to 180mg/dL.
In view of this, some clinicians recommend that insulin-treated patients "aim" for traces of glucose in their urine to avoid hypoglycemia. This virtually assures consistent hyperglycemia. Patients with non-insulin dependent diabetes mellitus or NIDDM who are treated with oral agents such as in the above case are at such low risk for hypoglycemia that they should "aim" for negative urine glucose concentrations at all times.
The most serious disadvantage of urine glucose tests is that they correlate poorly with concurrent blood glucose concentrations. This is because urine glucose concentrations are influenced by a patient's renal threshold for glucose, urinary retention, urine dilution or concentrations, and accurate testing.
Changes in urine glucose concentrations often lag behind changes in blood glucose concentration. The renal thresholds vary greatly from patient to patient which makes interpretation of urine tests even more difficult. In one study of 65 insulin-dependent diabetic patients, the renal threshold ranged from 54 to 180mg/dL (mean 130mg/dL). Renal thresholds tend to rise with age and with decreasing renal function, and may increase to more than 300 to 400mg/dL.
Ideally, when a patient is started on urine glucose concentrations and second-voided urine glucose concentrations should be measured to determine the patient's renal threshold for glucose. - National Poison Centre.
Source: The New Straits Times Press (Malaysia) Berhad
