Background: To determine the best HbA1c test interval strategy for detecting new type 2 diabetes mellitus (T2DM) cases in a healthy population, HbA1c test characteristics, risk stratification towards T2DM and cost effectiveness were considered.
Methods: State transition models were built to study the optimal screening interval for new cases of T2DM among each age- and BMI-stratified health population. Age was stratified into 30-44-, 45-59-, and 60-74-year-old age groups, and BMI was also stratified into underweight (<18.5 kg/m2), normal (18.5-25 kg/m2), overweight (25-30 kg/m2) and obesity (≥30 kg/m2). In each model, different HbA1c test intervals were compared to evaluate costs per quality-adjusted life year (QALY) and the incremental cost-effectiveness ratio (ICER). We compared intervals annually (current Japanese strategy), every three years (US and UK recommendations) and tailored to each risk stratification group, based on our previous work. All model parameters, including screening and treatment costs, complications and mortality rates and utilities, were applied from published studies. The willingness-to-pay threshold in the cost-effectiveness analysis was set to US $50,000/QALY.
Results: The HbA1c test interval for detecting T2DM in a healthy population varies by age and BMI. Three-year intervals were the most cost effective in obesity at all ages—30-44: $15,034/QALY, 45-59: $11,849/QALY, 60-74: $8,685/QALY—compared with the other two interval strategies. The three-year interval was also the most cost effective in the 60-74-year-old age groups—underweight: $11,377/QALY, normal: $18,123/QALY, overweight: $12,537/QALY—and in the overweight 45-59-year-old group; $18,918/QALY. In other groups, the screening interval for detecting T2DM was found to be longer than three years, as previously reported. Annual screenings were dominated in many groups with low BMI and in younger age groups. Based on the probability distribution of the ICER, QALY does not show much difference among any groups.
Conclusions: Annual screening to detect T2DM was not cost effective and should not apply to any population. The three-year screening interval was optimal among all elderly populations, the obesity at all ages and the overweight 45-59-year-old group. For the low BMI and younger age groups, the optimal HbA1c test interval can be longer than three years.