Systemic immune-inflammation index combined with ferritin can serve as a reliable assessment score for adult-onset Still's disease

Objective The diagnosis of adult-onset Still's disease (AOSD) is based on nonspecific symptoms and laboratory data, and several infectious, autoimmune, and malignant diseases must be ruled out. This study aimed to elucidate the value of various laboratory inflammatory scores, including the systemic immune-inflammation index (SID, C-reactive protein/albumin ratio (CAR), albumin/globulin ratio (AGR), prognostic nutritional index (PNI), and ferritin/erythrocyte sedimentation rate ratio (FER) as assessment factors for diagnosis and evaluation of disease activity in AOSD. Methods The medical records of patients suspected of AOSD between January 1999 and June 2019 were examined. The inflammatory scores were compared between AOSD and non-AOSD groups, and receiver operating characteristic (ROC) curve analysis was performed to evaluate diagnostic utility. Results A total of 164 patients diagnosed with AOSD had higher values of SII, CAR, and FER, as well as lower values of AGR and PNI, than non-AOSD patients (n = 61) . For an AOSD diagnosis, the area under the receiver operating characteristic curve (AUC) was 0.859 (95% confidence interval [CI], 0.806-0.911) for the SII, 0.769 (95% CI, 0.702-0.837) for the CAR, 0.749 (95% CI, 0.615-0.782) for the AGR, 0.699 (95% CI, 0.675-0.823) for the PNI, and 0.764 (95% CI, 0.693-0.834) for the FER, with optimal cut-off values of 2195.7, 1.8, 1.38, 48.8, and 17, respectively. The SII had the largest AUC and the highest specificity (91.5%). In further analysis, the AUC for the combination of SII and ferritin was 0.904 (95% CI, 0.863-0.945), with a cut-off value of 2615.4. Conclusions Laboratory inflammatory scores can be used as a practical tool for diagnosing AOSD. The SII and ferritin combination proved to be the most powerful assessment tool.