2.3 Self-monitoring of urine glucose
Some people may choose not to test their blood glucose. They may instead test for the presence of glucose in their urine as a measure of blood glucose control. In someone without diabetes, the amount of glucose in the blood does not reach such a high level that the kidneys start to transport it into the urine. This level is called the renal threshold and in most people, is about 10 mmol/l. If the level of glucose rises to above this amount in the blood of someone with diabetes, then glucose starts to appear in the urine. By testing their urine at regular intervals, someone with diabetes can see if the amount of glucose in their blood has risen above the normal range (i.e. 10 mmol/l) since they last passed urine. If their diabetes is well controlled, they would find most of their urine tests would be negative (i.e. no glucose in the urine). Of course, to be effective, this test assumes that the person has a normal renal threshold. If their kidneys do not start to remove glucose into the urine until the level of glucose in the blood reaches, say, 15 mmol/l, they may have negative urine tests (i.e. a ‘normal’ result) despite having poorly controlled blood glucose. This can occur commonly as people get older, and is described as having a high renal threshold. Sometimes, people have a low renal threshold, where glucose appears in the urine when the blood glucose level is normal. Both high and low renal thresholds can occur in healthy kidneys, and does not necessarily mean there is kidney damage, but it does mean that urine testing is not a suitable method for blood glucose monitoring.
Why would someone choose not to test their blood to check his or her diabetes control?
Blood testing can be painful. Some people with poor vision or manual dexterity problems (severe arthritis, for example) may not be able to use a glucose meter. Some people feel anxious about the results they get, especially if they do not know what to do about them. In addition, some GPs restrict the prescriptions of blood testing strips to people using certain types of diabetes treatments because of the costs of testing strips (as mentioned above).