title: Automated time-resolved immunofluorometric assay for Toxoplasma gondii-specific IgM and IgA antibodies: study of more than 130,000 filter-paper blood-spot samples from newborns.
abstract: BACKGROUND
  To screen for congenital toxoplasmosis, we developed a time-resolved immunofluorometric assay for the simultaneous detection of Toxoplasma gondii-specific IgM and IgA in filter-paper samples collected from newborns 4-7 days after birth.
  
  
  METHODS
  The assay was performed on the AutoDELFIA, and results were calculated based on the ToxoM WHO Third International Reference Serum. Comparison with an in-house mu-capture immunoassay was carried out retrospectively on filter-paper samples from children with confirmed congenital toxoplasmosis. Prospectively the assay was compared with a mu-capture immunoassay on 68 394 samples and a commercially available assay on another 69,467 samples. Before serum was requested from the newborn, positive samples were tested for IgA and IgM separately and in an IgM-immunosorbent agglutination assay developed for filter-paper samples.
  
  
  RESULTS
  Intra- and interassay variations (CVs) were 8% and 16%, respectively. The cutoff of 5 units/mL produced a 0.5% retest rate. The assay detected 13 of 18 (72%) samples from newborns diagnosed with congenital toxoplasmosis in the retrospective study. Prospectively, the assay identified 24 newborns who were later diagnosed with congenital toxoplasmosis. Results for all 24 cases were positive by the respective comparison method. No cases were detected solely by the IgA antibodies in the sample.
  
  
  CONCLUSIONS
  Neonatal screening for congenital toxoplasmosis can be automated by use of purified europium-labeled antigen for detection of T. gondii-specific IgM and IgA eluted from filter-paper samples.
authors.affiliation: Department of Clinical Biochemistry, Statens Serum Institut, 5 Artillerivej, DK-2300 Copenhagen S, Denmark.
authors.forename: Tina
authors.initials: T
authors.lastname: Sørensen
authors.forename: Johanne
authors.initials: J
authors.lastname: Spenter
authors.forename: Irakli
authors.initials: I
authors.lastname: Jaliashvili
authors.forename: Michael
authors.initials: M
authors.lastname: Christiansen
authors.forename: Bent
authors.initials: B
authors.lastname: Nørgaard-Pedersen
authors.forename: Eskild
authors.initials: E
authors.lastname: Petersen
mesh_terms: D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood*; D001322:Autoanalysis; D001800:Blood Specimen Collection; D002851:Chromatography, High Pressure Liquid; D004797:Enzyme-Linked Immunosorbent Assay; D015200:Fluoroimmunoassay; D006801:Humans; D007070:Immunoglobulin A / Q000097:blood*; D007075:Immunoglobulin M / Q000097:blood*; D007231:Infant, Newborn; D010209:Paper; D014122:Toxoplasma / Q000276:immunology*; D014125:Toxoplasmosis, Congenital / Q000175:diagnosis* / Q000276:immunology
chemical_list: D000913:Antibodies, Protozoan; D007070:Immunoglobulin A; D007075:Immunoglobulin M