Does the LDH/Albumin Ratio Bring Novelty? A Comparative Analysis with Inflammatory Indices and Combined Models in Adult-Onset Still's Disease

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Background/Objectives: The objective of this study was to evaluate the diagnostic accuracy of the lactate dehydrogenase-to-albumin ratio (LAR) in adult-onset Still’s disease (AOSD) and compare it with other inflammatory indices, using patients with fever of unknown origin (FUO) as a control group due to their overlapping clinical features with AOSD. The study also compared LAR’s diagnostic performance with other inflammatory indices like the serum immune-inflammatory index (SII), ferritin/erythrocyte sedimentation rate (FER), CRP/albumin ratio (CAR), platelet/lymphocyte ratio (PLR), and neutrophil/lymphocyte ratio (NLR), as well as its combinations with FER, PLR, and ferritin (LAR + FER, LAR + PLR, LAR + ferritin). Methods: A retrospective evaluation was conducted on 70 patients with fever of unknown cause and 78 patients with AOSD, admitted between January 2000 and December 2023 in a tertiary care hospital. Demographic, clinical, and laboratory characteristics were compared between the groups. ROC analysis provided cutoff values, sensitivity, and specificity for each inflammatory index. Results: ROC analysis showed significant p-values (p < 0.05) for indices other than LAR (p = 0.090) LAR + PLR (p = 0.806), and PLR (p = 0.634) in diagnosing AOSD. The highest specificity was found in LAR + ferritin (92.90%), and the highest sensitivity in CAR (100.0%). NLR, SII, FER, and LAR + FER were the indices with both sensitivity and specificity above 50%. LAR had a sensitivity of 76.90% and a specificity of 48.60%. The cutoff values were 3978.0 µg/L for ferritin and 70.98 for LAR. Significant statistical differences between AOSD and non-AOSD groups were observed for all indices except CAR (p = 0.133). Conclusions: LAR can differentiate AOSD patients from FUO, but its specificity is lower than most other indices. The diagnostic utility of these indices in clinical practice remains controversial.