title: A new method for determination of varicella-zoster virus immunoglobulin G avidity in serum and cerebrospinal fluid.
abstract: BACKGROUND
  Avidity determination of antigen-specific immunoglobulin G (IgG) antibodies is an established serological method to differentiate acute from past infections. In order to compare the avidity of varicella-zoster virus (VZV) IgG in pairs of serum and cerebrospinal fluid (CSF) samples, we developed a new technique of avidity testing, the results of which are not influenced by the concentration of specific IgG.
  
  
  METHODS
  The modifications introduced for the new VZV IgG avidity method included the use of urea hydrogen peroxide as denaturing reagent, the adaptation of the assay parameters in order to increase the sensitivity for the detection of low-level VZV IgG in CSF, and the use of a new calculation method for avidity results. The calculation method is based on the observation that the relationship between the absorbance values of the enzyme immunoassays with and without denaturing washing step is linear. From this relationship, a virtual absorbance ratio can be calculated. To evaluate the new method, a panel of serum samples from patients with acute and past VZV infection was tested as well as pairs of serum and CSF.
  
  
  RESULTS
  For the serum panel, avidity determination with the modified assay gave results comparable to standard avidity methods. Based on the coefficient of variation, the new calculation method was superior to established methods of avidity calculation.
  
  
  CONCLUSIONS
  The new avidity method permits a meaningful comparison of VZV IgG avidity in serum and CSF and should be of general applicability for easy determination of avidity results, which are not affected by the concentration of specific IgG.
authors.affiliation: Institute of Virology and Immunobiology, University of Würzburg, Versbacher Str. 7, 97078 Würzburg, Germany. ralf.kneitz@gmx.de
authors.forename: Ralf-Herbert
authors.initials: RH
authors.lastname: Kneitz
authors.forename: Jörg
authors.initials: J
authors.lastname: Schubert
authors.forename: Franz
authors.initials: F
authors.lastname: Tollmann
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Zens
authors.forename: Klaus
authors.initials: K
authors.lastname: Hedman
authors.forename: Benedikt
authors.initials: B
authors.lastname: Weissbrich
mesh_terms: D000208:Acute Disease; D000914:Antibodies, Viral / Q000097:blood / Q000134:cerebrospinal fluid / Q000276:immunology*; D000915:Antibody Affinity; D003289:Convalescence; D006562:Herpes Zoster / Q000276:immunology* / Q000821:virology; D014645:Herpesvirus 3, Human / Q000276:immunology*; D006801:Humans; D006861:Hydrogen Peroxide; D007124:Immunoenzyme Techniques; D007074:Immunoglobulin G / Q000097:blood / Q000134:cerebrospinal fluid / Q000276:immunology*; D008433:Mathematics; D011489:Protein Denaturation / Q000276:immunology; D012680:Sensitivity and Specificity; D012984:Software; D013997:Time Factors; D014508:Urea
chemical_list: D000914:Antibodies, Viral; D007074:Immunoglobulin G; D014508:Urea; D006861:Hydrogen Peroxide