Modelling the cost-effectiveness of adopting risk stratified approaches to extended screening intervals in the national diabetic retinopathy screening programme in Scotland

Aims:
To assess the cost-effectiveness of adopting risk stratified approaches to extended screening intervals in the national diabetic retinopathy screening programme in Scotland.
Methods:
A continuous-time hidden Markov model was fitted to national longitudinal screening data to derive transition probabilities between observed non-referable and referable retinopathy states. These were incorporated in a decision model simulating progression, costs and visual acuity outcomes for a synthetic cohort with covariate distribution matching that of the Scottish diabetic screening population. The cost-effectiveness of adopting extended (two-year) screening for groups identified as low risk was then assessed over a 30 year time horizon.
Results:
Individuals with a current grade of no retinopathy on two consecutive screening episodes face the lowest risk of progressing to referable disease. For the cohort as a whole, the incremental cost per QALY gained for annual versus biennial screening ranged from ~£74,000 (for those with no retinopathy and a prior observed grade of mild or observable background retinopathy) to ~£232,000 per QALY gained (for those with no retinopathy on two consecutive screening episodes). The corresponding incremental cost-effectiveness ratios in the subgroup with Type 1 diabetes were substantially lower; ~£22,000 to £85,000 per QALY gained respectively.
Conclusions:
Biennial screening for individuals with diabetes who have no retinopathy is likely to deliver significant savings for a very small increase in the risk of adverse visual acuity and quality of life outcomes. There is greater uncertainty regarding the long-term cost-effectiveness of adopting biennial screening in younger people with Type 1 diabetes.