Long-Term Adherence to Automated Bolus Calculators

Software for insulin dosing has been implemented in blood glucose meters to assist patients treated with multiple daily injections (MDI) in insulin dose decision making. These advanced blood glucose meters, also known as automated bolus calculators (ABCs), have been demonstrated to improve metabolic control and treatment satisfaction in adults with poorly controlled type 1 diabetes (T1D) in randomized studies of up to 12 months’ duration.^1-3

However, patient behavior may be affected by study participation even when studies are conducted in a setting resembling routine clinical practice. ⁴ Therefore, to investigate adherence to ABC use in real-life conditions, we conducted a follow-up study of ABC use and metabolic control in previous StenoABC participants 12 month after study completion.

StenoABC was a 12-month, randomized, parallel group clinical study of the effects of advanced carbohydrate counting (ACC) guided by an ABC compared with unassisted ACC (ie, insulin bolus dose size determination based on mental calculations) in ACC-naïve adults with suboptimally controlled, MDI-treated T1D. ¹ A total of 168 patients were enrolled (baseline HbA1c 9.0% ± 0.8%) and 130 completed the study. The main finding of the study was that patients who used an ABC (ABC group) achieved significantly greater reduction in HbA1c compared with patients who relied on mental calculations (MC group) (–0.5% vs −0.2%, P = .033). After study completion, patients in the MC group were offered an ABC and patients in the ABC group were encouraged to continue device use.

One year later, we contacted patients by letter, inviting them to participate in a follow-up study. We developed a simple questionnaire for retrospective recording of ABC use. In all, 128 letters, questionnaires, consent forms and stamped addressed envelopes were sent out (1 patient from the original cohort had died and 1 was lost to follow-up). In addition, we obtained HbA1c values from electronic patient records.

We received 67 questionnaires and consent forms (response rate 52%), 38 from former ABC group members and 29 from former MC group members (P = .156). Questionnaire responders were significantly (P < .05) older than nonresponders (52 vs 44 years), had longer diabetes duration (25 vs 20 years) and lower HbA1c at StenoABC entry (8.8 vs 9.1%), whereas there was no significant difference (P > .05) in sex (41 vs 59% male) or change in HbA1c during StenoABC participation (–0.5 vs −0.4%). The overall trends within the ABC group and the MC group were similar. Within 12 months after StenoABC completion, 9 patients had switched from MDI to insulin pump therapy. Among the remaining 58 MDI users, 43 (74%) were still using the ABC; 26 (45%) were using the ABC exclusively, whereas 17 (29%) combined ABC use with mental calculations or experience-based dosing. Only 4 respondents (7%) were applying the principles of ACC but determining the bolus dose size by means of mental calculations, that is, they had implemented ACC in their daily diabetes management but not ABC use. The outstanding 5 respondents (9%) based all bolus size decisions on previous experience. There were no significant differences in usage patterns between former ABC and MC group members. Only few patients had changed usage pattern in the preceding 12 months, that is, if they were frequent users the first month they were also frequent users at the end of the year and vice versa.

Changes in HbA1c from StenoABC completion to follow-up were insignificant within the ABC group (0.1% [95% CI −0.2 to 0.3%], P = .588) and the MC group (–0.1% [95% CI −0.3 to 0.1%], P = .337) as well as between groups (P = .331).

The results of this follow-up study, that is, high levels of device adherence and maintenance of improvements in metabolic control, confirm previous findings in a more diverse population including patients who were in good metabolic control and patients who were already counting carbohydrates when the ABC was introduced. Since this study was partly based on retrospective questionnaires, the conclusions may, however, be limited by nonresponse and recall bias.

In summary, 12 months after completion of the StenoABC study, ABC adherence among previous participants was high (74% of follow-up study respondents were using the device). Furthermore, improvements in HbA1c obtained during StenoABC were maintained after return to routine clinical practice.