Cystic Fibrosis (CF) is an autosomal recessive disorder that results from defective activity of the CF transmembrane conductance regulator (CFTR protein). Newborns are
typically asymptomatic, though some may present with a meconium ileus or poor weight gain. If an infant is not screened and/or is left untreated, symptoms begin to appear in childhood and can include progressive lung disease, pancreatic insufficency, and poor nutritional uptake/weight gain.
Incidence: ~1/3200; more common in Caucasians (esp. Northern European descent)
Diagnosis: The newborn screen measures immunoreactive trypsinogen (IRT), an enzyme secreted by the pancreas. Infants who have an elevated IRT on the initial screen will be identified as having a borderline result and a repeat screen will be requested on this initial report (this is known as the IRT/IRT method). If the baby has two elevated IRT levels on the screen, follow up with sweat chloride testing is needed to confirm the diagnosis.
Treatment: Affected children require life-long enzyme treatment, respiratory therapy, and monitoring by both primary care and speciality providers.
If treated promptly, children with cystic fibrosis can be expected to develop and gain
weight appropriately. Even with treatment, bacterial endobronchitis, pancreatic insufficiency, and infertility can occur. Affected children should be monitored for pulmonary function and proper growth and weight gain.
False Positives: Common, especially in babies who spend time in the NICU. Some of these babies will end up being carriers. Maryland does not incorporate DNA testing for CFTR as part of the newborn screen.