<h4>Purpose</h4>To evaluate the predictive value of serum cystatin C and indirect bilirubin (IBIL), both individually and in combination, for sight-threatening diabetic retinopathy (STDR) in type 2 diabetes mellitus (T2DM).<h4>Methods</h4>Retrospective cross-sectional study. This evidence concerns the gene CST3 and diabetic retinopathy.