Association between HbA1c status relative to individualized targets and estimated 28-day diabetes-related cost in older outpatients with diabetes: a single-center cross-sectional study

Background and aims In older adults with diabetes, HbA1c below the lower limit of individualized targets may reflect intensive or potentially excessive treatment rather than favorable glycemic control. The association between this status and diabetes-related cost remains unclear. We examined the association between HbA1c status relative to individualized targets and estimated 28-day diabetes-related cost. Methods This single-center cross-sectional study included 117 outpatients aged ≥ 65 years. Patients were classified as below the lower limit, within/meeting the individualized target, or above the target. Diabetes-related cost, defined as net drug cost plus diabetes-related care management fees, was the primary outcome; net drug cost was analyzed as a component of this outcome. Medication costs were standardized to 28 days. We performed group comparisons and exploratory multivariable regression using ln-transformed diabetes-related cost. Sensitivity analysis using ln(cost + 1) included zero-cost patients. Results Nine patients were below the lower limit, 60 were within/meeting the target, and 48 were above the target. Median diabetes-related cost was highest in the below-lower-limit group, followed by the above-target and within/meeting-target groups (27,075, 10,732, and 3,663 JPY/28 days, respectively; p < 0.001). In exploratory regression excluding zero-cost patients, the adjusted cost ratio for below-lower-limit versus within/meeting-target status was 2.03 (95% confidence interval, 1.13–3.62; p = 0.018). In sensitivity analysis including zero-cost patients, the estimate was imprecise and no longer statistically significant. Conclusion Patients below the lower limit of individualized HbA1c targets had the highest unadjusted estimated 28-day diabetes-related cost, with frequent insulin use and care management fees. Medication review may be considered in this subgroup.