MATERIALS AND METHODS: Eighty-eight patients diagnosed with AS were enrolled from the Rheumatology Unit at Baghdad Teaching Hospital. Participants were categorized into two groups based on disease status: inactive (n = 44) and active (n = 44). Additionally, 44 matched healthy individuals were included as controls. Comprehensive medical histories were obtained, including disease duration, body mass index, sex, and age. Laboratory parameters related to the disease-such as C-reactive protein, human leukocyte antigen (HLA-B27), and rheumatoid factor-were also measured. Serum IL-41 levels were quantified using an enzyme-linked immunosorbent assay.

RESULTS: The study revealed a significant difference in levels of IL-41 in patients with AS (17.721±0.705 ng/L) compared to controls (8.495±0.984 ng/L; P = 0.009). The mean serum IL-41 concentration was highest in the active group (23.037±5.268 ng/L), followed by the inactive group (12.411±1.672 ng/L; p = 0.001) and controls (8.495±0.984 ng/L). Serum IL-41 levels demonstrated strong validity for diagnosing AS, with a cutoff value of ≥ 9.35 ng/mL and an area under the curve of 0.991. The sensitivity, specificity, and accuracy were 97.7%, 79.5%, and 92.38%, respectively (p = 0.002).