Despite the negative results of our community-based study of the link between self-monitoring of blood glucose (SMBG) and glycemia (1), Kolb et al. (2) commented on the overall concordance of our study and several other observational studies. They also suggest that we might have missed a positive impact of SMBG since new users in our cohort were not differentiated from either prevalent users or never users.
In our prospectively followed 531 type 2 diabetic patients (1), 92 who self-monitored at study entry stopped without subsequent detriment to their A1C (median [interquartile range] 7.0% [6.3–8.0] vs. 7.3% [6.4–8.4] at annual visits before and after stopping, respectively; mean change +0.1%; P = 0.47). By contrast, 103 patients who started SMBG during follow-up improved their A1C (7.5% [6.3–9.1] vs. 7.2% [6.2–8.4] before and after, respectively; P = 0.032). The mean change (−0.3%) is similar to that in both the new-user cohort of Karter et al. (3) and the meta-analysis of the few randomized controlled trials of SMBG (4).
The remaining 336 patients either performed SMBG throughout follow-up (SMBG+; n = 306) or did not (SMBG−; n = 30). We calculated updated mean A1Cs over 5 years for patients in these two groups by baseline diabetes treatment. For diet-treated subjects, the medians were 6.6% (interquartile range 5.9–7.1) for SMBG+ (n = 92) and 6.6% (5.9–7.0) for SMBG− (n = 17). For those taking oral hypoglycemic agents (OHAs), the medians were 7.4% (6.8–8.2) (n = 181) and 7.0% (6.5–7.5) (n = 13), respectively (P = 0.24). All 33 insulin-treated patients who were not performing SMBG at baseline monitored at some time during follow-up.
Previously, we have shown in the same longitudinal cohort of 531 patients (5) that the median A1C was reduced by 0.3% when diet-treated patients started OHA and by 1.5% when OHA-treated patients started insulin. The apparent benefit of initiating SMBG might, therefore, reflect intensification of treatment. However, when our patients started SMBG, 85% continued with the same treatment, 12% reduced treatment, and 3% intensified treatment.
The largest randomized controlled trial (6) has found that the glycemic improvement observed in non–insulin-treated patients allocated to SMBG occurred in the first 3 months, with a steady state thereafter. These and our longer-term data suggest that SMBG may have only a relatively transient beneficial effect on glycemia. There is a need for strategies that ensure its sustainability.
