Performance of a four-step newborn screening strategy for CF in the Dutch screening program: WS 10.4

Workshop. Since May 1, 2011, newborn screening for Cystic Fibrosis (NBSCF) is part of the Dutch NBS program Objectives: To assess the validity of the four-step screening strategy when applied in a routine newborn screening program. Methods: NBSCF was carried out as a 4-step strategy (Immunotrypsinogen (IRT)/Pancreatitis-associated Protein (PAP)/DNA-analysis for 35 CFTR mutations/extended gene analysis (EGA) (Thorax 2012;67: 289). As safety net EGA-analysis was performed in samples with IRT ≥ 100 μg/L but no CF mutations. In 2013 the strategy was adapted: besides newborns with two mutations, either disease-causing or of unknown clinical relevance, also newborns with one disease-causing mutation were referred to a designated CF centre for further diagnosis. Data analysis was carried out as if the screening strategy was adapted during the whole period of data collection (May 1, 2011 to January 1, 2016). CF centres reported results of sweat tests and CF patients not identified by NBSCF in the NBS-registry. Carriers and newborns with CFSPID were considered false positives. Before data-analysis a cross checkwas performed comparing data in the NBS- and the Dutch CF patient-registry. Results: 819,518 newborns, 99.95% of all newborns, were screened for CF; in 8,131 IRTwas ≥60 μg/L, in 1,079 DNA-analysis followed PAP analysis; 121 had 2 CF mutations; EGA analysis was performed in 85 samples with 1 CF mutation, in 474 as safety net. 193 were screen-positive. CF was confirmed in 122, we found 27 CFSPID, 37 carriers. CF was excluded in 7. A false negative screening test was reported for 16 (4 with meconium ileus (MI)), in 8 caused by PAP values < cut-off levels. We calculated a specificity of 99.99%, PPV 63%, CF/CFSPID ratio of 5/1 and a sensitivity of 91% (without MI). Conclusion: PAP as additional marker in NBSCF appears to lead to an excellent true/false positive rate and the finding of a low number of carriers. Lower PAP cut-off from 1–7-2016 can improve sensitivity to standards of care.