A retrospective investigation of the platelet-to-lymphocyte ratio as a potential indicator in early rheumatoid arthritis

Background The platelet-to-lymphocyte ratio (PLR) has been suggested as a biomarker for inflammation and disease activity in rheumatoid arthritis (RA). However, current findings on its correlation with the Disease Activity Score 28 (DAS28) remain inconsistent. This study aimed to explore the correlation between PLR and DAS28. Methods This retrospective study analyzed 433 consecutive inpatients with early RA at Xingtai People’s Hospital between January 2022 and January 2024. Of these, 72.06% were women, with a mean age of 52.52 ± 14.20 years. All patients met the 2010 American College of Rheumatology/European League Against Rheumatism criteria and had symptoms <2 years. To further explore the association between the PLR and the DAS28, multiple regression analyses were conducted, followed by generalized additive models. Results After adjusting for potential confounding factors, we found that for every 50-unit increase in PLR, DAS28 based on erythrocyte sedimentation rate (ESR) increases by 0.126 ( P < 0.001) and DAS28 based on C-reactive protein (CRP) increases by 0.145 ( P < 0.001). The general trends remained consistent across the PLR tertile groups, from the lowest to the highest. A nonlinear correlation was detected between PLR and DAS28-ESR and DAS28-CRP, with an inflection point for PLR of 254. When PLR was less than 254, it exhibited a significantly positive correlation with DAS28-ESR and DAS28-CRP ( P < 0.001 for both). Conclusion This study revealed a threshold effect: in patients with early RA (ERA), PLR is positively associated with DAS28-ESR and DAS28-CRP only when PLR is below 254. Above that level, the pattern may not hold, illustrating a nonlinear relationship.