Severe lung disease in children with cystic fibrosis missed in newborn screening

BackgroundCystic fibrosis (CF) is now routinely diagnosed through newborn screening (NBS), but the tests employed in the USA have been evolving for two decades as missed cases become recognized and lab methods improve in association with more knowledge about CF genetics. New Jersey was among the first states to implement CF NBS in 2001 when it introduced the original two-tiered method that combined measurements of immunoreactive trypsinogen (IRT) with detection of the principal pathogenic variant (F508del) in the cystic fibrosis transmembrane conductance regulator (CFTR) gene.ObjectiveWith continuation of the IRT/DNA (F508del) algorithm for two decades and identification of screening false negative children, we decided to examine the condition of some missed cases with special attention to their respiratory status.MethodsTo strengthen the arguments for quality improvement in New Jersey's CF NBS program, we reviewed and evaluated false negative cases to determine the potential extent of preventable patient suffering as a consequence of delayed diagnoses.ResultsFive children with CF who had false negative screening results were studied in detail. In each case there was a different cause of the negative screening results. They all had clinically significant/severe lung disease, ranging from chronic cough with CF pathogens on respiratory culture at a young age to respiratory failure.ConclusionThis case series highlights the consequences of false negative screening results, which served as the impetus to upgrade New Jersey's CF NBS algorithm. Implemented changes include lowering the IRT cutoff to 70 ng/mL and expanding to a 139 variant CFTR panel. In 2023, a floating IRT cutoff is anticipated to be implemented.