From the Guidelines
Newborns should be tested for cystic fibrosis (CF) as soon as possible after 10 days of age, ideally by the end of the neonatal period (four weeks of age), if no prenatal testing was performed and they have a positive CF newborn screen. This recommendation is based on the most recent and highest quality study, which suggests that sweat chloride testing should be performed bilaterally and when the infant weighs >2 kg, and is at least 36 weeks of corrected gestational age 1. The initial screening is typically done via a blood test, and if the results are positive, follow-up testing such as a sweat chloride test or genetic testing is performed to confirm the diagnosis.
Key Considerations
- Newborns with a positive CF newborn screen should have sweat chloride testing performed as soon as possible after 10 days of age 1
- Infants with presumptive CF identified through newborn screening should not have treatment delayed while efforts to establish a diagnosis of CF are initiated 1
- A diagnosis of CF can be made if the sweat chloride value is ≥60 mmol/L, and individuals with clinical features consistent with CF who have a sweat chloride <30 mmol/L indicates that CF is unlikely 1
Testing and Diagnosis
- Sweat chloride analysis should be performed within a few hours of sweat collection 1
- Individuals presenting with a positive newborn screen, symptoms of CF, or a positive family history, and sweat chloride values in the intermediate range (30-59 mmol/L) on two separate occasions may have CF and should be considered for extended CFTR gene analysis and/or CFTR functional analysis 1
- CFTR genetic testing should be performed if the CFTR genotype was not available through the screening process or is incomplete 1
From the Research
Newborn Screening for Cystic Fibrosis
- Newborn screening for cystic fibrosis (CF) is typically performed using an immunoreactive trypsinogen (IRT)-DNA-IRT protocol 2.
- If no prenatal testing was performed, newborns are usually screened for CF through a heel prick test, which measures IRT levels in dried blood spots 3.
- The screening process typically involves an initial IRT test, followed by a second IRT test and DNA analysis if the initial test is abnormal 4.
Age of Testing
- The initial IRT test is usually performed within the first 24-48 hours of life 4.
- A second IRT test is typically performed 7-14 days after the initial test, or after 18-24 days in some cases 5, 4.
- If the diagnosis is not definitive, a sweat chloride test may be repeated at 12 months, and if possible, at 6 and 24 months of life, along with extended CFTR sequencing to detect rare mutations 6.
Follow-up and Diagnosis
- Infants with inconclusive CF diagnosis should be followed up at 3,6, and 12 months of life, and every year thereafter, in a CF reference center 6.
- Any symptoms indicative of CF require immediate reevaluation of the diagnosis 6.
- The use of whole genome sequencing may enhance personalized, precision care for CF patients, beginning in infancy 2.