title: Newborn screening for cystic fibrosis by use of a multiplex immunoassay.
abstract: BACKGROUND
  Since its beginnings, newborn screening for cystic fibrosis (CF) using an assay for immunoreactive trypsinogen (IRT) has been plagued by a high rate of false-positive results (screen positive, diagnosis negative), despite attempts to reduce this rate by use of altered cutoffs and second-tier DNA testing. IRT exists as 2 isoforms: IRT1 and IRT2, with IRT2 being more closely aligned with pancreatic disease, including CF. Assay standardization between programs is a continuing problem because the IRT assays currently in use variously recognize either 1 or both isoforms. Here we report the development of a multiplexed assay for both forms of IRT simultaneously.
  
  
  METHODS
  Using 2 different Luminex bead sets, we developed assays for each IRT isoform separately and then combined them. Using the sum of IRT1 and IRT2 values (IRT1+IRT2), we compared the results with a CF kit currently in use.
  
  
  RESULTS
  In a sample set consisting of 16 cases confirmed positive for CF, we established a cutoff at >97 microg/L total IRT. Seven of 8 carriers with 1 CF mutation screen-positive by the standard method were also screen-positive by IRT1+IRT2. Of 32 cases screen-positive by standard IRT, 11 were screen-negative by IRT1+IRT2. None of these 11 cases had CF mutations identified by the screening program.
  
  
  CONCLUSIONS
  These data indicate that the multiplex method with specificity for 2 isoforms of IRT has performance comparable to that of a standard IRT method and the advantage of improved standardization by detection of the 2 isoforms.
authors.affiliation: New York State Department of Health, Wadsworth Center, Biggs Laboratory, Albany, NY, USA.
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Lindau-Shepard
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Pass
mesh_terms: D003550:Cystic Fibrosis / Q000175:diagnosis*; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007231:Infant, Newborn; D015997:Neonatal Screening / Q000379:methods*; D020033:Protein Isoforms / Q000276:immunology; D014362:Trypsinogen / Q000276:immunology
chemical_list: D020033:Protein Isoforms; D014362:Trypsinogen