Quality assessment of a screening algorithm for diabetic retinopathy: prolongation of screening intervals with minimal effect of HbA1c and arterial hypertension on the length of intervals

PURPOSE: At Steno Diabetes Center Copenhagen (SDCC), diabetic retinopathy (DR) screening intervals are based on quantification of retinal lesions. Screening intervals are, for the milder forms of DR, prolonged to 2-3 years. The purpose of the present study was to evaluate the effect of the prolongation on developing unexpected events and to evaluate the effect of HbA1c and arterial hypertension.

METHODS: We assessed 18 972 screening intervals from 6000 patients from 1/1-2003 to 1/5-2017 for occurrence of unexpected events, defined as: (1) DR progression requiring treatment, at the following screening date, and (2) DR-related hospital contact within the planned interval. We modelled the effect of several risk factors for developing unexpected events in a Cox regression. Furthermore, we assessed the risk of unexpected events in a logistic regression analysis using cubic splines to model the effect of HbA1c , stratified by arterial hypertension status.

RESULTS: 16 283 (86%) intervals followed the planned interval and among those, only 86 (0.5%) experienced unexpected events. Intervals of dysregulated patients (86% of all intervals) did not experience more unexpected events, compared with well-regulated patient intervals (Hazard Ratio: 1.12, 95% CI: 0.55-2.27). We found a nonlinear effect of HbA1c on the risk of unexpected events which peaked around HbA1c levels of 80 mmol/mol. Having arterial hypertension slightly increased the risk of unexpected events.

CONCLUSIONS: The present study supports the validity of the current algorithm. We found no increased risk of unexpected events among dysregulated intervals but a nonlinear effect of HbA1c . Age, diabetes duration and diabetes type were significantly associated with unexpected events.