Serum Retinol-binding Protein 3 as a Potential Biomarker for Diabetic Retinopathy Severity: A Cross-sectional Study

Introduction: Diabetic Retinopathy (DR) is one of the leading causes of visual impairment worldwide. Its progression is influenced by complex metabolic, inflammatory and neurodegenerative mechanisms. Retinol-binding Protein 3 (RBP3), a retina-specific glycoprotein essential for the visual cycle, has recently gained attention due to its potential neuroprotective and anti-inflammatory roles. Reduced RBP3 levels may contribute to retinal dysfunction, making it a possible biomarker for DR risk stratification. Aim: To assess serum RBP3 levels among Type 2 Diabetes Mellitus (T2DM) patients and determine its association with the severity of DR, glycaemic control and systemic inflammation. Materials and Methods: A hospital-based cross-sectional study was conducted at Nootan Medical College and Research Centre, Visnagar, Gujarat, India, from January 2023 to February 2024, in collaboration with the Departments of Biochemistry, Ophthalmology, and Medicine. A total of 100 T2DM patients (aged 45-65 years) were enrolled. Detailed retinal examinations were performed to classify DR severity. Serum RBP3 levels were measured using Enzyme-Linked Immunosorbent Assay (ELISA). Glycated Haemoglobin (HbA1c) and high-sensitivity C-Reactive Protein (hs-CRP) were evaluated as indicators of glycaemic status and systemic inflammation. Statistical analysis was performed using MedCalc software, with p-value <0.05 considered significant. Results: The study included 100 patients with T2DM presenting with vision problems, with a mean age of 55.04±4.47 years (range: 45-65 years); 55% were female, and 45% were male. DR was present in 87% of participants, with mild non proliferative DR being the most common stage. Serum RBP3 levels showed a strong inverse correlation with DR severity (p-value <0.0001). Significant negative correlations were observed between RBP3 and HbA1c (r=–0.9136, p-value <0.0001) and between RBP3 and hs-CRP (r=–0.9654, p-value <0.0001). Conclusion: Serum RBP3 levels show a significant inverse association with the severity of DR, hyperglycaemia, and inflammation. These findings indicate that lower serum RBP3 levels are associated with more advanced retinopathy, poorer glycaemic control, and heightened systemic inflammation. RBP3 may serve as a promising biomarker for early detection and risk assessment in DR. Larger, longitudinal studies with predictive analysis are required to establish its diagnostic and therapeutic relevance.