Nonlinear Correlation Between Prognostic Nutritional Index and Disease Activity of Rheumatoid Arthritis: A...

The prognostic nutritional index (PNI) is a composite marker reflecting the nutritional and inflammatory status. Its association with disease activity in rheumatoid arthritis (RA) remains incompletely understood. This study aimed to investigate the relationship between PNI and RA disease activity.

A total of 984 RA patients were enrolled and stratified into three groups according to PNI tertiles. Univariate analysis and linear regression models were performed to evaluate the association between PNI and disease activity scores (DAS28-ESR/DAS28-CRP). A two stage (segmented) linear regression model was used to identify potential inflection points in the relationship.

Univariate analysis showed that PNI was significantly negatively correlated with both DAS28-ESR (β = -0.043, p < 0.001) and DAS28-CRP (β = -0.045, p < 0.001). After adjusting for demographic characteristics, inflammatory markers, and therapeutic drugs, this negative correlation remained significant in the fully adjusted model (DAS28-ESR: β = -0.034, p < 0.001; DAS28-CRP: β = -0.044, p < 0.001). Segmented regression identified a non-linear relationship with an inflection point at approximately 45.0. Below this threshold, the negative association was markedly stronger (DAS28-ESR: β = -0.073; DAS28-CRP: β = -0.069). Above the inflection point, the association weakened and became non-significant for DAS28-ESR (β = -0.012, p > 0.05), while for DAS28-CRP it remained significant but attenuated (β = -0.020, p < 0.05).

PNI is independently negatively associated with RA disease activity, with a notably stronger effect when PNI is below 45. PNI may serve as a simple and effective biomarker for assessing inflammation and nutritional status in RA patients, and may help identify patients with greater nutritional-inflammatory burden.