Tight glycaemic control is the cornerstone of treatment in diabetes and self-testing can help to ensure good blood glucose control and avoid severe hypoglycaemia – Professor Andrew Farmer illustrates how
Good control of blood glucose is important in preventing or delaying the complications of diabetes, including heart disease, renal problems and retinopathy. However, many people do not have good control of their blood glucose and need to monitor and adjust their treatment depending on the results.
Levels of blood glucose are either directly measured through self-testing with blood glucose meters, or indirectly with glycated haemoglobin or HbA1c.
• Measurement of HbA1c at up to three monthly intervals is recommended by NICE to gain an overall picture of control, with subsequent adjustment of treatment if this is unsatisfactory.1
• HbA1c closely matches average glucose levels over the preceding six to eight weeks.
• People with type 1 diabetes and insulin-treated type 2 diabetes need their treatment adjusting more frequently, and should be aware of their glucose measurements from regular self-testing.
Hand-held meters allow convenient day-to-day self-testing at home, work and leisure. More recent meters have minimised the volume of the blood sample required to reduce the possibility of error, and can warn of inaccurate results with error messages. However, the tests are not as accurate as laboratory tests and can have errors of 15-20%
Who needs to self-test and how often?
Self-testing should be made available to people with diabetes when the information obtained through testing can be used to:
• Actively adjust treatment.
• Enhance understanding of diabetes.
• Assess the effectiveness of the management plan on blood glucose control.2
The amount of testing needed will depend on the insulin regimen used and whether the control is intended to be tight. With long-acting insulin treatment injected once daily in type 2 diabetes, then self-testing can be carried out as little as twice a week. However, as the complexity of the treatment regimen increases, then testing may be required throughout the day to adjust insulin dose before each meal and monitor the effects of physical activity.
Despite support and encouragement, some people who need to self-test find the procedure unacceptable. In these circumstances, urine testing remains a possibility, although it provides only very limited information.
A UK based, randomised trial found no evidence of benefit from regular testing for well-controlled patients with non-insulin treated type 2 diabetes.3 Use of self-testing for these patients should increasingly be focused on particular stages of the disease and driven by events rather than on a need for regular self-testing.4
There are some circumstances where self-testing may be helpful, although the evidence base for such use is not strong. For example:
• A short period of self-testing in the context of a well-structured education programme for newly diagnosed patients may provide useful information about the impact of day-to-day activities on blood glucose level.
• Self-testing may also be used to guide self-adjustment of sulfonylurea glucose lowering medications for some very motivated individuals.
• Thirdly, it may be helpful when blood glucose control is deteriorating despite treatment with oral medication as it may help prepare people for the addition of insulin to their treatment, as well as motivate efforts to modify lifestyle.
Which patients do not need to self-test?
Non-insulin treated patients with well-controlled type 2 diabetes do not need to routinely self-test their blood glucose levels.
The cost of self-monitoring blood glucose (SMBG) in people with type 2 diabetes in England is uncertain, but probably around £30 million a year of which at least half could be saved by adhering to previous guidelines and by applying the findings from recent research.2
Monitoring in non-insulin treated diabetes
Three-monthly HbA1c testing is recommended by NICE for patients with diabetes who are not well controlled,1 and can provide a useful guide to the success of lifestyle measures and titration of oral hypoglycaemic medication (e.g. metformin or thiazolidenediones). Less frequent testing is needed if control is below the recommended targets, with annual testing currently recommended.
If expertise is available to help support its use, then short periods of blood glucose self-testing may be helpful, although a strong evidence-base is currently lacking.
• Oral glucose lowering medication such as sulfonylurea can be titrated using two to three fasting tests a week to review glycaemic control.
• Impact of lifestyle on glycaemic control for newly diagnosed patients within a structured education programme can be established with a period of testing before and after physical activity and eating different types of food.
Self-testing may be needed for people with type 2 diabetes if there are concerns about hypoglycaemia. Consistently low (<4mmol/L) blood glucose readings when hypoglycaemic symptoms are absent may point to the need to adjust medication. In addition, some patients will need to self-test during periods of intercurrent illness. There may also be a need for self-testing if there are concerns about the safety of activities, such as driving.
Professor Andrew Farmer is professor of general practice in the department of primary health care at the University of Oxford
Table 1 Table 2 Table 3 Self testing