Median CGM use was 7.0 days/week (interquartile range 6.3–7.0) at 6 months and 6.8 days/week (interquartile range 5.8–7.0) at 12 months (see online appendix supplemental Table S1, available at http://care.diabetesjournals.org/cgi/content/full/dc09-0846/DC1
). Use at 12 months did not vary with baseline A1C level (Spearman r
= −0.10; P
Among subjects with baseline A1C ≥7.0%, mean change in A1C from baseline to 12 months was −0.4 ± 0.6% (P < 0.001), similar to the change from baseline to 6 months. The reduction in A1C occurred mainly in the first 8 weeks and then remained relatively stable through the next 44 weeks (supplemental Fig. S1). Among subjects with baseline A1C <7.0%, A1C remained within the target range over the entire 12 months of the study (6.4, 6.3, and 6.4% at baseline, 6 months, and 12 months, respectively; P = 0.42 for change from baseline to 12 months).
A severe hypoglycemic event was experienced by 8 (10%) of the 83 subjects (9 events) during the first 6 months and 3 subjects (4%; 3 events) in the second 6 months. The rate of severe hypoglycemic events fell from 21.8 events per 100 person-years during the first 6 months to 7.1 events per 100 person-years (95% CI 0–16.7) during the second 6 months (P = 0.18). The rate was not associated with baseline A1C (Spearman r = −0.004; P = 0.97). In subjects with baseline A1C ≥7%, the incidence fell from 20.5 events per 100 person-years in the first 6 months to 12.1 events per 100 person-years in the second 6 months, whereas in the A1C <7% cohort, the incidence fell from 23.6 events per 100 person-years to no events during the second 6 months (supplemental Fig. S2).
The median amount of time per day with glucose in the range of 71–180 mg/dl increased significantly (P = 0.02) from baseline to 12 months, reflecting a decrease in both hypoglycemia and hyperglycemia. Similar trends were seen both in subjects with baseline A1C ≥7.0% and in those with baseline A1C <7.0% (). The increase in time in range was seen during both daytime and nighttime (supplemental Table S2). Variability assessed with the SD of glucose values (P = 0.02) and mean amplitude of glycemic excursions (P = 0.03) was reduced with CGM use from baseline to 12 months. Body weight, daily insulin dose, and frequency of daily blood glucose meter tests did not change meaningfully during the study.
Clinical features and metabolic control measures