Cystic fibrosis newborn screening (CF-NBS) start-up in Flanders (Belgium): report of first evaluation after 3 years

In January 2019, CF-NBS was started in Flanders (Belgium) involving 2 screenings labs using an IRT-DNA algorithm with a limited CFTR mutation panel and an IRT/IRT failsafe. Diagnosis is confirmed by sweat chloride (SCl) and CFTR mutation analysis. Methods: IRT was measured in dried blood spots (DBS) collected 72–96 hours after birth. If IRT was above the P99 cut-off, 12 CFTR mutations were searched for. Screen positive newborns (IRT>P99 and 1 or 2 mutations) were referred to a CF centre for quantitative pilocarpine iontophoresis (QPI). For IRT >P99.9 with negative mutation screening, a failsafe is provided with repeat IRT before day 21 (IRT-D21). For meconium ileus (MI), CF diagnostics are done irrespective of NBS result. CF centres provided feedback to the screening labs after diagnostic assessment. Results: In 2019 and 2020 (analysis of 2021 ongoing), 125,732 newborns were screened (coverage 99.9%). Sixty-eight (0.056%) had raised IRT plus at least 1 mutation. Three babies were screen +ve from the failsafe arm (IRTIRT) and 5 were sent for a QPI after ultra-high IRT, no mutation but missing the repeat IRT-D2. This resulted in 76 referrals for QPI. CF was confirmed in 24/76 babies (23/68 and in 1/5 newborn after the failsafe net without repeat IRT-D21; 43 babies were carriers, 3 were CRMS/CFSPID (CF metabolic syndrome/CF screen positive inconclusive diagnosis), 6 no CF/ no carrier. Median age at initial visit in the CF centre was 20 days and 23 days at diagnosis. CF centres reported no missed cases so far. Only 1 baby with MI had a negative CF-NBS, however this was not considered as false negative as per protocol. Based on these results, sensitivity was 100%, PPV 0.31 (calculated without CFSPID), and CF/CFSPID ratio was 8. Discussion: Performance of the program has been in agreement with ECFS standards. By June 2022, results will be extended to 3 years of screening. Based on current results, the IRT cut-off will be adapted to P99.2 to further improve the PPV.