Association Between Prognostic Nutritional Index and Disease Activity in Patients with Rheumatoid Arthritis: A Retrospective Cohort Study.

The prognostic nutritional index (PNI), derived from serum albumin and lymphocyte count, reflects immunonutritional status and may be influenced by systemic inflammation. This study examined the association between PNI and disease activity in rheumatoid arthritis (RA). A total of 730 patients fulfilling the 2010 ACR/EULAR criteria were retrospectively analysed. Demographic, clinical, and laboratory data were collected; disease activity and disability were assessed using the DAS28-CRP and Health Assessment Questionnaire (HAQ). Correlation analyses, multivariable linear regression, ROC analyses, subgroup testing, and mediation analyses were performed. The mean age was 56.2±12.5 years and 76.3% were women. Median DAS28-CRP was 3.38, with 11.2% classified as having high disease activity. Mean PNI was 54.0±5.34. PNI was significantly lower in patients with high DAS28-CRP and in severe HAQ categories (p<0.01). PNI correlated negatively with DAS28-CRP, HAQ, CRP, ESR, and disease duration (all p<0.01). However, PNI was not independently associated with DAS28 or HAQ in adjusted regression models, whereas CRP and ESR remained significant predictors. ROC performance of PNI was modest (AUC 0.65-0.67). Associations were stronger in older adults and in men, and mediation analyses indicated that CRP and ESR largely explained the PNI-DAS28 relationship. Lower PNI was associated with greater RA burden, but this association appears to be largely driven by systemic inflammation.