Objective

To determine if baseline diabetic retinopathy (DR) severity mediates the relationship between health insurance status and DR progression.

Design

Retrospective cohort study.

Subjects

Seven hundred sixteen patients aged ≥ 18 years with a diagnosis of type 1 or 2 diabetes mellitus, and a diagnosis of nonproliferative DR (NPDR) were identified from the electronic health record of a tertiary academic center between June 2012 and February 2022.

Methods

NPDR severity at baseline was the proposed mediator in the relationship between insurance status and proliferative DR (PDR) progression. Logistic regression was used to determine the association between insurance status and NPDR severity at baseline, and Cox proportional hazards regression was used to assess the association between insurance status and time to PDR progression. To analyze the mediation effect of NPDR severity at baseline, a counterfactual approach, which decomposes a total effect into a natural direct effect and a natural indirect effect was applied.

Main outcome measures

Time to progression from first NPDR diagnosis to first PDR diagnosis.

Results

Of the 716 patients, 581 (81%) had Medicare or private insurance, 107 (15%) had Medicaid, and 28 (4.0%) were uninsured at their baseline eye visit. Uninsured or Medicaid patients had a higher proportion of moderate or severe NPDR at their baseline eye visit and a higher proportion of progression to PDR. After adjusting for confounders and NPDR severity at baseline, patients who were uninsured had significantly greater risk of progression to PDR compared with that of patients with Medicare/private insurance (hazard ratio [HR]: 2.63; 95% confidence interval [CI]: 1.10-6.25). Patients with Medicaid also had an increased risk of progression to PDR compared with that of patients with Medicare/private insurance, although not statistically significant (HR: 1.53; 95% CI: 0.81-2.89). NPDR severity at baseline mediated 41% of the effect of insurance status (uninsured vs. Medicare/private insurance) on PDR progression.

Conclusions

Patients who were uninsured were more likely to have an advanced stage of NPDR at their baseline eye visit and were at significantly greater risk of progression to PDR compared with patients who had Medicare or were privately insured. Mediation analysis revealed that differences in baseline NPDR severity by insurance explained a significant proportion of the relationship between insurance status and DR progression.

Financial disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.