Composite inflammatory indices for monitoring treatment response and predicting organ involvement in brucellosis

Reliable biomarkers for monitoring treatment response in brucellosis remain limited because conventional inflammatory markers do not always reflect disease activity. This study aimed to evaluate changes in composite inflammatory indices before and after treatment and to investigate their potential role in monitoring treatment response and predicting organ involvement. This observational study included 52 adult patients with brucellosis who received antimicrobial therapy. The systemic immune-inflammation index (SII), systemic inflammation composite index (SICI), platelet inflammation composite index (PICI), and routine inflammatory markers were evaluated before treatment and after completion of therapy. A total of 52 patients with brucellosis were included, of whom 18 (34.6%) had organ involvement. Following treatment, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) decreased significantly compared with pretreatment values (both p < 0.001). Similarly, SICI and PICI were significantly reduced after treatment (both p < 0.001), whereas SII remained unchanged. Patients with sacroiliitis were older than those with hepatic involvement ( p = 0.009) and had higher eosinophil counts ( p < 0.001). In ROC analysis, ESR showed the highest discriminatory performance for predicting organ involvement (AUC = 0.715, 95% CI: 0.571–0.859, p = 0.011), followed by PICI (AUC = 0.686, 95% CI: 0.539–0.834, p = 0.028). In contrast, CRP, SII, and SICI did not demonstrate significant predictive performance. SICI and PICI may serve as biomarkers for monitoring treatment response in brucellosis. While ESR showed the strongest discriminatory performance for organ involvement in ROC analysis, composite inflammatory indices may provide complementary information for assessment.