Self-monitoring of blood glucose in patients with type 2 diabetes, particularly those who are not on insulin, has long been controversial.
- Studies have been inconsistent in terms of showing a benefit to SMBG in these patients, and thus, some clinicians do not have their patients monitored. Others find the information useful in patient care decisions and, thus, do have patients SMBG, although perhaps at a lower frequency than someone using insulin.
A meta-analysis of nine randomized controlled trials found a small, but significant, decrease in HbA1c after 6 months in those who used SMBG. At least two other trials have shown no significant difference in HbA1c changes in those who used SMBG for 12 months. Another meta-analysis, also involving nine trials, showed conflicting results. Five of the trials showed small improvements in HbA1c with SMBG, whereas the other four showed no difference. Two other meta-analyses found that most studies showed a small but significant decrease in HbA1c in those who utilize SMBG and have baseline HbA1c >8%. There was no difference in those with a baseline HbA1c <8%.
In those who use SMBG, increased frequency does not appear to be of additional benefit.
There are potential disadvantages associated with SMBG. For instance, some data have shown an increased risk for depression. Also, SMBG can become expensive for patients, even if they have health insurance, because the company may or may not cover the supplies. Although patients can often obtain the meters for little cost due to rebates, the ongoing supplies can be expensive.
Of course, anyone who uses SMBG must be properly trained on the procedure if the results are going to be considered reliable. This would include things such as ensuring the meter is coded correctly, correct test strips are used, test site is prepped appropriately, etc.
Finally, if everyone is going to go through the trouble of SMBG, we need to know that the meters our patients are using are accurate. You may be surprised to learn that the FDA minimum accuracy requirement for meters to be marketed is ±20% for glucose values >75 mg/dL, at least 95% of the time. For values <75 mg/dL, accuracy of ±15% is required. Thus, there could be a clinically significant difference between SMBG values and standard lab values. Therefore, utilizing other markers, such as HbA1c, in conjunction with SMBG values provides a more complete, and potentially accurate, picture.
Most guidelines, continue to recommend SMBG in patients with type 2 diabetes not on insulin therapy, at least in conjunction with broader self-management education. By recognizing the strengths and weaknesses associated with SMBG, clinicians can tailor their recommendations to individual patients. Although clinicians will typically utilize SMBG values in treatment decisions, patients do not usually act on them. Perhaps if more patients were taught how to institute changes based on SMBG, and they were willing and able to do so, then the benefit of SMBG may be greater