Assay Methodology Drives Interleukin-17 Heterogeneity in Psoriasis: A Meta-Analysis
Abstract
Psoriasis is a chronic immune-mediated skin disorder in which interleukin-17 (IL-17) plays a central role in disease pathogenesis through the TNF-α/IL-23/IL-17 inflammatory axis. Despite broad consensus on IL-17 elevation in psoriasis, reported circulating levels vary markedly across studies, and the contribution of assay methodology to this variability remains underexplored. This systematic review and meta-analysis evaluated circulating IL-17 levels in psoriasis patients compared to healthy controls, with a primary objective of estimating the pooled effect size and a secondary objective of identifying assay methodology as a potential driver of inter-study heterogeneity. A systematic search of PubMed and Scopus identified 26 eligible studies involving 1,466 psoriasis patients and 1,083 healthy controls. The pooled standardised mean difference was 1.22 (95% CI: 0.78 to 1.66, p < 0.001), confirming significantly elevated circulating IL-17 in psoriasis patients. Substantial heterogeneity was observed (I² = 95.31%), prompting comprehensive moderator analysis. Diagnostic tool type (ELISA versus non-ELISA) and study sample size emerged as significant moderators, while geographic region, psoriasis subtype, sex distribution, patient age, and methodological quality score did not significantly contribute to variability. Sensitivity analysis confirmed the robustness of the pooled estimate, and no publication bias was detected. Incomplete reporting of disease severity, treatment history, and disease duration across included studies limited full characterisation of heterogeneity sources. These findings support the role of IL-17 as a biomarker and therapeutic target in psoriasis, and indicate that assay methodology represents a key source of variability in circulating IL-17 measurement. Standardised immunoassay protocols and comprehensive clinical reporting are needed in future primary research to improve the reliability and comparability of IL-17 estimates across studies.