Measuring serum concentrations of interleukin-33 in atopic dermatitis is associated with potential false positive results.

BACKGROUND In the search for valid biomarkers in inflammatory diseases, cytokine serum concentrations are often measured by enzyme-linked immunosorbent assay and correlated to disease activity. Interleukin-33 is a relatively newly described cytokine, which holds a promising potential as a biomarker for different diseases including atopic dermatitis. However, interfering human anti-animal IgG antibodies and heterophilic antibodies might give rise to false positive or negative results that often go unnoticed. FINDINGS We performed a three-step validation of commercially available and widely used human interleukin-33 enzyme-linked immunosorbent assay kit with serum samples from eight atopic dermatitis patients and five healthy controls. Through addition of unspecific animal IgG (rabbit, mouse, goat and bovine) and unspecific human IgG to the assay diluent, we disclosed false positive values in 12 out of 13 samples. CONCLUSION This study show that the present human interleukin-33 enzyme-linked immunosorbent assay kit might give rise to a high prevalence of false positive values if not validated. This inaccuracy is easily eliminated with a simple set of validation steps.