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.
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: Melissa R Miller; David Soave; Weili Li; Jiafen Gong; Rhonda G Pace; Pierre-Yves Boëlle; Garry R Cutting; Mitchell L Drumm; Michael R Knowles; Lei Sun; Johanna M Rommens; Frank Accurso; Peter R Durie; Harriet Corvol; Hara Levy; Marci K Sontag; Lisa J Strug Journal: J Pediatr Date: 2015-03-11 Impact factor: 4.406
Authors: William J Kimberling; Michael S Hildebrand; A Eliot Shearer; Maren L Jensen; Jennifer A Halder; Karmen Trzupek; Edward S Cohn; Richard G Weleber; Edwin M Stone; Richard J H Smith Journal: Genet Med Date: 2010-08 Impact factor: 8.822