Which laboratory tests are most useful in confirming a diagnosis of Adult-Onset Still's Disease?

The most useful laboratory tests to confirm a diagnosis of adult-onset Still's disease (AOSD) include markedly elevated serum ferritin levels, raised inflammatory markers such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), and leukocytosis with neutrophilia. Serum ferritin is particularly valuable, often showing levels several times above the normal range, which supports the diagnosis in the appropriate clinical context ¹. Additionally, liver function tests may reveal mild elevations in transaminases, and exclusion of infections and other rheumatological diseases through serological tests is essential to rule out differential diagnoses (Bagnari et al., 2010; Kadavath and Efthimiou, 2015).

Other laboratory findings that assist but are not diagnostic include negative rheumatoid factor (RF) and antinuclear antibody (ANA) tests, which help differentiate AOSD from other autoimmune conditions. Elevated serum interleukin-18 and glycosylated ferritin fraction reduction have been described in recent literature as promising markers but are not yet standard in clinical practice (Poursac et al., 2022).

In summary, the diagnosis of AOSD relies on a combination of clinical features supported by laboratory evidence of systemic inflammation, especially very high serum ferritin, raised ESR/CRP, neutrophilic leukocytosis, and exclusion of other causes.