Association between Red Cell Distribution Width to Platelet Ratio and Disease Activity among Iraqi Patients with Systemic Lupus Erythematosus

Background: The link between red blood cell distribution width-to-platelet ratio (RPR) and disease activity in systemic lupus erythematosus (SLE) is not well understood. Aim:  To investigate the association between RPR levels and disease activity in SLE. Methods: This was a case-control study conducted at Baghdad Teaching Hospital, Medical City from July 2020 to March 2021. Seventy SLE patients were compared with 70 healthy controls. The diagnosis was made using the American College of Rheumatology SLE criteria. Results: SLE patients had a mean age of 35.2±12.03 years, while controls had a mean age of 36.3±9.9 years (P=0.5). Females represent 97.1% of SLE patients and 88.6% of controls. The average disease duration was 4.98±0.05 years. The disease activity index (SLEDI) was 16.4±4.8. SLE patients had a lower platelet count than controls, and the median (IQR) of RDW was larger than that of controls. SLE patients had a greater median (IQR) of RPR than controls (0.058; 0.04-0.07 vs. 0.045; 0.039-0.053). The RPR and SLEDAI showed strong positive association. The optimal cutoff point for distinguishing SLE patients from controls was 0.0455, with 79% sensitivity and 51% specificity. The RPR was not significantly affected by sociodemographic or clinical factors. Conclusion: The RPR was positively correlated with disease activity in SLE patients, and may be a valid measure to differentiate between SLE patients and healthy controls. Sociodemographic and other clinical characteristics do not significantly affect RPR.