Background: Diabetes mellitus (DM) is a group of metabolic disorders characterized by chronic hyperglycemia. It is caused by defective insulin production or resistance of the cells to insulin. The chronic hyperglycemia leads to damage of different organs, especially eyes, kidneys, nerves, heart, and blood vessels. MicroRNAs (miRNAs) are small noncoding regulatory ribonucleic acids (RNA). Many studies have showed the association between miRNA 126 and complications of DM including diabetic retinopathy (DR). Objective: Assessing the ability of circulating miRNA 126 to be used as diagnostic biomarker of both proliferative diabetic retinopathy (PDR) and non-proliferative diabetic retinopathy (NPDR). Methodology: This case-control study was conducted on 20 DR (PDR & NPDR) patients, 20 DM patients without DR and 20 apparently healthy controls that were recruited from Research Institute of Ophthalmology-RIO. Identification and quantification of plasma miRNA126 was performed by real-time PCR. Results: MiRNA 126 expression is significantly decreased in PDR group when compared to healthy control. Its expression in PDR is less than in NPDR, expression in NPDR is less than in DMC, and expression in healthy people is higher than in other groups (P value < 0.001). ROC curve was done for healthy control group versus DMC, PDR and NPDR groups and showed that the area under the curve (AUC) was 1.0 for all groups with sensitivity and specificity 100%, confidence interval (CI) was 95% with upper and lower limit (1.0-1.0). Best cut off point of miRNA-126 was 5.44, 4.44, 4. 88 for DMC, PDR and NPDR respectively. There is also a high significant increase between each group and control regarding hemoglobin A1C (HbA1c). There is significant increase between PDR and control regarding triglycerides (TG). Conclusion: miRNA 126 can differentiate between the PDR, NPDR, DMC and control group and could be considered a non-invasive diagnostic parameter.

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