title: Measuring serum concentrations of interleukin-33 in atopic dermatitis is associated with potential false positive results.
abstract: 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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Dermatology and Venereology, Aarhus University Hospital, P.P. Ørumsgade 11, 8000 Århus C, Denmark ; Department of Clinical Medicine, Aarhus University, 8000 Århus C, Denmark.
authors.forename: Uffe
authors.identifier: 0000-0003-0824-6307
authors.initials: U
authors.lastname: Nygaard
authors.affiliation: Department of Dermatology and Venereology, Aarhus University Hospital, P.P. Ørumsgade 11, 8000 Århus C, Denmark.
authors.forename: Christian
authors.initials: C
authors.lastname: Vestergaard
authors.affiliation: Department of Dermatology and Venereology, Aarhus University Hospital, P.P. Ørumsgade 11, 8000 Århus C, Denmark.
authors.forename: Claus
authors.initials: C
authors.lastname: Johansen
authors.affiliation: Department of Dermatology and Venereology, Aarhus University Hospital, P.P. Ørumsgade 11, 8000 Århus C, Denmark.
authors.forename: Mette
authors.initials: M
authors.lastname: Deleuran
authors.affiliation: Department of Clinical Medicine, Aarhus University, 8000 Århus C, Denmark ; Department of Biomedicine, Aarhus University, 8000 Århus C, Denmark.
authors.forename: Malene
authors.initials: M
authors.lastname: Hvid
keywords: Anti-animal IgG antibodies; Atopic dermatitis; Enzyme-linked immunosorbent assay; Heterophilic antibodies; Immunoassay; Interference; Interleukin-33