Self-monitoring of blood glucose is an important component of modern therapy for diabetes and of proven efficacy for glucose control in type 1 diabetes (insulin-dependent diabetes mellitus) and type 2 diabetes patients using insulin. The benefit in patients with type 2 diabetes not in need for insulin therapy, though, has not yet been conclusively demonstrated. The authors of the Cochrane Collaboration have reviewed the scientific literature on this topic.
Diabetes mellitus is a rather common disease in the Western industrialized countries: 6 to 8% of the total population have diabetes (2000: 177 million patients worldwide), and these numbers are estimated to become even higher in the future. Self-monitoring of blood glucose (SMBG) is recommended for people with diabetes and their health care professionals in order to achieve glycemic control–to prevent hypoglycaemia as well as hyperglycaemia and, by the latter, so preventing (mainly microvascular) diabetes complications, as retinopathy, nephropathy, and neuropathy. The aim of SMBG is to get detailed information about blood glucose levels at many time points and so to enable maintenance of a glucose level as constant as possible by more precise regimens: by adjustment of diet, physical activity, and insulin doses to improve glycemic control on a day-to-day basis.
There is an ongoing debate on the benefit of SMBG in non-insulin dependent diabetes mellitus (NIDDM). At the time being, these patients should have a visit to a general practitioner or diabetes nurse in a three-month interval for the evaluation of glycemic control. It has been suggested that SMBG might possibly replace these 3-monthly visits, leading to greater independence for the patients, a better understanding of their disease and therefore a better compliance with medical treatment and better motivation for lifestyle changes.
The authors of a recent Cochrane review have chosen data from six randomised controlled (one additionally blinded for outcome assessor) studies from 1990 up to 2005 to search for a final conclusion. Four of the trials compared SMBG with usual laboratory testing, one trial compared SMBG with self-monitoring of urine glucose and one three-armed trial compared SMBG with self-monitoring of urine glucose and usual care.
The mean methodological quality of studies was low (assessment by a score list by two independent reviewers). Two of the six studies reported a statistical significant lowering effect on levels of haemoglobin A1c (HbA1c). One of these trials, though, included also changes of diet and lifestyle by additional educational programs, so a clear assignment of result to intervention could not be made. There were only two studies reporting other outcome measures (quality of life, well-being, patients‘ satisfaction), and these effects did not reach statistic significance.
The authors conclude, as far as the level of evidence is concerned, from the reviewed studies that there is only moderate evidence for SMBG having a positive effect on HbA1c levels in NIDDM patients, and no proven evidence for such effects on fasting plasma glucose, quality of life, patients‘ satisfaction and well-being.
There are several possible explanations for this only moderate evidence: The group sizes varied largely between studies (from 12 to 689), with the two biggest largest showing the significant effects (113 and 345 patients in the intervention groups, respectively). Furthermore, the frequency of monitoring blood glucose differed between the studies, diabetes duration and baseline HbA1c levels were also different between the studies, which all may have contributed to the different results. Additionally, patients taking part in a randomised controlled trial might be more motivated in both the intervention and control group to improve their behaviour by the knowledge that outcome measures are being observed.
Overall, to assess these potential benefits a large and well designed randomised controlled (control group versus intervention group) trial is required. This long-term trial should also investigate additional patient-related outcomes like quality of life, well-being and patient satisfaction, and provide adequate education to the patient to allow SMBG to be effective. Furthermore, there should be studied subgroups of patients according to age, diabetes duration and baseline HbA1c values. With these analyses it can be determined whether SMBG is more effective in a special group of patients, like newly diagnosed patients or poorly controlled patients.