Prospective study of inflammatory biomarkers and risk of diabetic retinopathy in the diabetes control and complications trial.

IMPORTANCE This study demonstrates that increasing quintiles of baseline high-sensitivity C-reactive protein (hsCRP) level may be associated with higher risk of incident clinically significant macular edema, the leading cause of vision loss in working-aged individuals in North America. OBJECTIVE To determine whether baseline levels of hsCRP and intercellular adhesion molecule 1 (ICAM-1) predict development and progression of diabetic retinopathy (DR), clinically significant macular edema (CSME), retinal hard exudates, and proliferative DR in the Diabetes Control and Complications Trial (DCCT) cohort. DESIGN The DCCT was a large multicenter randomized controlled clinical trial. SETTING Twenty-nine medical centers in the United States and Canada. PARTICIPANTS The DCCT population consisted of 1441 subjects with type 1 diabetes mellitus aged 13 to 39 years at study entry. INTERVENTION We measured levels of hsCRP, ICAM-1, vascular cell adhesion molecule 1, and tumor necrosis factor α receptor 1 in stored baseline blood samples. MAIN OUTCOME MEASURES We assessed the association of levels of hsCRP, ICAM-1, vascular cell adhesion molecule 1, and tumor necrosis factor α receptor 1 with incident DR end points ascertained from grading of standardized 7-field stereoscopic retinal color photographs taken at baseline and every 6 months during follow-up. RESULTS After adjustment for randomized treatment assignment and other factors, we observed a statistically significant association between hsCRP and risk of CSME, with a relative risk (RR) for the top vs bottom quintile of 1.83 (95% CI, 0.94-3.55; P for trend = .01). Similarly, for the development of retinal hard exudates, the RR for the top vs bottom quintile of hsCRP level was 1.78 (95% CI, 0.98-3.25; P for trend = .004), whereas for ICAM-1 level, the RR comparing the top vs bottom quintiles was 1.50 (95% CI, 0.84-2.68; P for trend = .05). There were no statistically significant associations between baseline VCAM-1 or tumor necrosis factor α receptor 1 levels and risk of any of the DR end points. CONCLUSIONS AND RELEVANCE After adjusting for known risk factors, increasing quintiles of baseline hsCRP level may be associated with higher risk of incident CSME and macular hard exudate in the DCCT cohort. Circulating levels of ICAM-1 may also be associated with the development of retinal hard exudates.