title: Performance of 14 rubella IgG immunoassays on samples with low positive or negative haemagglutination inhibition results.
abstract: BACKGROUND
  Rubella IgG testing is routinely done in prenatal care and seroepidemiological studies. Recently concern was raised that seropositivity rates were decreasing questioning vaccination policies. Manufacturers of rubella IgG assays and authors of seroepidemiological studies use different cut-offs for the definition of seropositivity. As rubella virus circulation is reduced since many years, seronegativity rates might be overestimated using an inappropriate cut-off.
  
  
  OBJECTIVE
  Using different cut-off definitions we compared fourteen current rubella IgG immunoassays for sensitivity and qualitative result concordance in samples with low positive or negative haemagglutination inhibition (HI) titre.
  
  
  METHODS
  150 clinical samples from patients and health care workers were included in the study. All samples were measured in 14 different rubella IgG immunoassays. Seropositivity was defined using recombinant rubella IgG immunoblot as reference standard.
  
  
  RESULTS
  The concordance of qualitative results using the manufacturers cut-off definitions was 56.4% if grey-zone results were analysed separately and 69.8% if grey-zone results were defined as positive. Using universal cut-offs of 10 IU/ml or 15 IU/ml the concordance was 70% and 61.4% respectively. Using the different cut-off definitions up to 71 out of the 124 immunoblot-positive samples tested negative in the immunoassays. The mean coefficient of variation (CV) of quantitative results in positive samples was 51% (range 19-113%).
  
  
  CONCLUSIONS
  Determination of rubella immunity by measurement of rubella-IgG in a population with high vaccination coverage with current assays leads to a high number of false negative results. The value of routine rubella antibody testing in countries with high vaccination coverage should be discussed.
authors.affiliation: Institute of Virology, University Medical Center Freiburg, Germany. Electronic address: daniela.huzly@uniklinik-freiburg.de.
authors.forename: Daniela
authors.initials: D
authors.lastname: Huzly
authors.affiliation: Institute of Virology, University Medical Center Freiburg, Germany.
authors.forename: Ingeborg
authors.initials: I
authors.lastname: Hanselmann
authors.affiliation: Institute of Virology, University Medical Center Freiburg, Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Neumann-Haefelin
authors.affiliation: Institute of Virology, University Medical Center Freiburg, Germany.
authors.forename: Marcus
authors.initials: M
authors.lastname: Panning
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000914:Antibodies, Viral / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D005188:False Negative Reactions; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007074:Immunoglobulin G / Q000097:blood*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012412:Rubella virus / Q000276:immunology*; D012680:Sensitivity and Specificity; D016036:Seroepidemiologic Studies; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral; D007074:Immunoglobulin G
keywords: Assay comparison; CRS; Rubella; Seroepidemiologic studies