The study included a cohort of patients (≥ 18 years) with type 1 or 2 diabetes (T1D or T2D) from a pilot DR screening program at Oslo University Hospital (OUH), Norway, conducted during the period December 2019 to January 2021.
Patients were mainly referred by general practitioners (GPs) who had received information about the pilot project (12 patients were referred by another affiliated health institution). GPs were asked to refer patients without known treatment-dependent DR who were not already followed by an ophthalmologist. A total of 90 patients (180 eyes) were included, including 12 with type 1 diabetes mellitus (T1DM) and 78 with type 2 diabetes mellitus (T2DM), which roughly reflects the estimated prevalence of type 1 and type 2 diabetes mellitus in the Norwegian population.22. We obtained written informed consent from all patients included between December 2019 and January 2021. The Regional Committee for Medical and Health Research Ethics concluded that the project fell outside the scope of the Norwegian Health Research Act (reference: 28857). The OUH Institutional Data Protection Officer approved the study (reference: 20/00571), which complied with current guidelines and regulations.
All patients were examined at the Department of Ophthalmology of the OUH. Color fundus photography was performed using a CLARUS™ 700 camera, Zeiss (Carl Zeiss Meditec AG, Jena, Germany). Foveal and optic disc centered photographs were obtained, both with 133° field of view. Diabetic maculopathy based on fundus photography was classified as follows: no maculopathy (0), presence of MA within one disc diameter (DD) of the foveola (1), and hard exudates within one DD of the foveola (2).
6 × 6 mm OCT radial scans of the macula were obtained using the NIDEK RS-3000 Advance OCT retinal scanner (NIDEK CO., LTD, Gamagori, Japan). In this study, the presence of intraretinal cysts and/or subretinal fluid in the central area of the macula, within one disc diameter of the foveal center, was qualitatively determined in our study by two experienced ophthalmologists (ESS, DF).
In the pilot screening for DR, we used a combined screening strategy in which OCT was performed in addition to fundus photography on all 90 enrolled patients. The existing screening strategy for DR in our department was to perform OCT only when fundus photography showed diabetic maculopathy. Subsequently, patients were asked to return for OCT on another day to assess for the presence of DME. The prevalence of diabetic maculopathy identified by fundus photography and the prevalence of DME detected by OCT in the pilot screening were determined. These prevalence rates, together with the DME/diabetic maculopathy ratio, were then used in cost analyses for both screening strategies.
We performed a cost analysis of DR screening using fundus photography and OCT combined on the same day (combined screening strategy) or on different days (existing sequential screening strategy). For sequential days, all fundus photography costs were included, while OCT costs were based on the presence of diabetic maculopathy. We also estimated the total cost of true positives for the presence of DME. These analyses involved different key parameters such as prevalence rates and imaging costs to assess the stability of our cost estimates under different scenarios.
The Diagnosis Related Group (DRG) is a system that classifies patients into different groups, taking into account factors such as diagnosis and treatment. The goal is to standardize the reimbursement process for public health services. In short, DRGs are designed to reflect the relative cost of treating patients with similar conditions. Each DRG is assigned a relative weight or severity level based on the average resources required to treat patients in that group. Hospitals are reimbursed based on the DRG assigned to each patient. The reimbursement amount is calculated by multiplying the hospital’s base payment rate by the relative weight of the assigned DRG. This payment system provides hospitals with incentives to manage resources efficiently and provide cost-effective care while ensuring appropriate reimbursement for services rendered.
The economic cost values of fundus photography and OCT were collected by assessing the DRG weights associated with the screening model (Table 1). This also constituted the direct costs in our estimation, although the OCT costs did not include more than consultation costs. Based on national guidelines, from an extended healthcare perspective, we included some indirect costs, e.g. return transport costs, costs associated with the patient’s time spent at the screening centre and travel time. We collected transport costs and patient time costs from the Norwegian Medicines Agency (NOMA) database (Legemiddelverk, 2021)22This database serves as a centralized repository of regulatory information and documentation for healthcare professionals, regulatory authorities and the general public.
In the sequential screening model, we summed the product of the DRG weight and fundus photography costs and the percentage of patients with diabetic maculopathy who had OCT on a scheduled date. For the combined screening model, we summed the direct costs of screening (DRG-weighted costs) for all patients. For both screening models, we then added the costs of transportation to and from the screening center, while the sequential screening model also included the costs of traveling to the second examination with OCT. We estimated patient time for fundus photography alone to be 1.5 h, for OCT alone to be 1.25 h, and for fundus photography and OCT combined to be 1.58 h. We multiplied these estimated times by the cost of patient time from the NOMA database and added the product to the total cost.
In a deterministic sensitivity analysis, we assessed the effect of a range of values on our results. In a one-way sensitivity analysis, we assessed the impact of higher or lower sensitivity of fundus photography on the cost per patient with diabetic maculopathy, the total cost of detecting DME, and overall costs. For the cost of OCT, we assessed the impact of increasing this cost in a two-way sensitivity model and varied the percentage of diabetic maculopathy.
