Paeds · respiratory-sleep-and-airway
Cystic fibrosis: diagnosis and screening
Also known as CF diagnosis · Newborn bloodspot screening for cystic fibrosis · Sweat chloride test · CFTR mutation testing · Mucoviscidosis
Fellowship guide to diagnosing and screening for cystic fibrosis in children: recognising the child whose salty skin, chronic wet cough, greasy stools and poor growth should trigger a sweat test; how newborn bloodspot screening with immunoreactive trypsinogen and CFTR mutation panels finds most infants before symptoms; confirming the diagnosis with the sweat chloride test and genetic analysis using the Cystic Fibrosis Foundation and ECFS criteria; interpreting an intermediate sweat chloride and the CRMS/CFSPID equivocal-screen category; the differential from other causes of failure to thrive and chronic suppurative lung disease; the meconium ileus, pseudo-Bartter and false-negative-screen traps; and the ANZ, UK and North American differences in screening protocols.
On this page
Study tools
Your progress
Saved on this device.
Practise this topic
Target exams
Red flags
- A newborn with meconium ileus (bilious vomiting, abdominal distension, failure to pass meconium) — this is cystic fibrosis until proven otherwise and needs a sweat test and genetics even if the newborn screen is pending or negative
- A dehydrated infant or child with hypochloraemic, hypokalaemic metabolic alkalosis and no vomiting — pseudo-Bartter syndrome from salt loss is a classic CF presentation, especially in hot weather
- A positive newborn screen result — arrange urgent referral to a specialist CF centre for a confirmatory sweat test rather than reassuring or delaying, because early diagnosis improves nutrition and outcome
- Failure to thrive with a chronic wet or productive cough, or recurrent or persistent pneumonia at the same or multiple sites — do a sweat test rather than repeating antibiotics
- Rectal prolapse, salty-tasting skin, nasal polyps in a young child, or a sibling with cystic fibrosis — each should prompt a sweat test regardless of a normal newborn screen
Life stages
Care settings
Clinical exam formats
Board mappings
- General and Community Paediatrics
- Respiratory medicine and suppurative lung disease
- Genetic and metabolic disease in childhood
- Current 2026 PREP curriculum — Learning goal 5: Clinical assessment – essential general paediatrics
- Renewed curriculum for first-year trainees from 2027 — Learning goal 8: Chronic and complex conditions
- Paediatric respiratory medicine and genetic diagnosis competencies
- Clinical Applications
- Respiratory medicine and multisystem genetic disease
- Long Cases
- Short Cases
- Chronic disease assessment scenarios
- 4. Professional skills and knowledge: Patient management
- 8. Children with complex health needs and disability
- Respiratory: Recognises and investigates suppurative lung disease and failure to thrive
- Foundation of Practice (FOP)
- Applied Knowledge in Practice (AKP)
- Respiratory medicine; genetics and newborn screening
- Clinical
- History and management planning
- Chronic respiratory and multisystem disease in childhood
- General Pediatrics Content Outline — Domain 17: Respiratory System
- General Pediatrics Content Outline — Domain 9: Genetics and Dysmorphology
- General Pediatrics Content Outline — Domain 15: Nutrition and Gastroenterology
- Patient Care 1: History and Physical Examination
- Patient Care 4: Clinical Reasoning
- Medical Knowledge 1: Clinical Knowledge
- Systems-Based Practice: population health and newborn screening
- Practice-Based Learning: use of diagnostic guidelines
- Medical Expert
- Communicator
- Health Advocate
- Scholar
- Pediatrics: Core EPA — Assess and investigate the child with chronic respiratory or nutritional disease
Overview & Definition
Picture the six-week-old whose parents mention that she tastes salty when they kiss her, has passed greasy, foul stools since birth, and has barely gained weight despite feeding well, with a rattly cough that has never quite cleared. That combination — salt, malabsorption and a wet chest in a baby who is not thriving — is the clinical shorthand for cystic fibrosis, and it should send your hand straight to a sweat test. [5] [1]
Cystic fibrosis is an autosomal recessive multisystem disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator, the CFTR gene on chromosome seven. CFTR is a chloride channel at the surface of epithelial cells, and when it fails, secretions across the airways, pancreas, gut, sweat glands and reproductive tract become thick and dehydrated. The disease is named for the fibrotic, cyst-like change once seen in the pancreas. [6] [5]
Why this matters at fellowship level is that diagnosis is time-critical. Finding cystic fibrosis before irreversible lung damage or malnutrition sets in changes the child's whole trajectory, so the examinable skill is knowing both how the screening pathway works and when to reach for a sweat test yourself in a child whose screen was negative or was never done. [10] [1]
References12ShowHide
- [1]Farrell PM, White TB, Ren CL, et al. Diagnosis of Cystic Fibrosis: Consensus Guidelines from the Cystic Fibrosis Foundation. J Pediatr, 2017.PMID 28129811
- [2]Farrell PM, White TB, Howenstine MS, et al. Diagnosis of Cystic Fibrosis in Screened Populations. J Pediatr, 2017.PMID 28129810
- [3]Sosnay PR, White TB, Farrell PM, et al. Diagnosis of Cystic Fibrosis in Nonscreened Populations. J Pediatr, 2017.PMID 28129813
- [4]Castellani C, Duff AJA, Bell SC, et al. ECFS best practice guidelines: the 2018 revision. J Cyst Fibros, 2018.PMID 29506920
- [5]Elborn JS. Cystic fibrosis. Lancet, 2016.PMID 27140670
- [6]Cutting GR. Cystic fibrosis genetics: from molecular understanding to clinical application. Nat Rev Genet, 2015.PMID 25404111
- [7]Grosse SD, Boyle CA, Botkin JR, et al. Newborn screening for cystic fibrosis: evaluation of benefits and risks and recommendations for state newborn screening programs. MMWR Recomm Rep, 2004.PMID 15483524
- [8]Comeau AM, Accurso FJ, White TB, et al. Guidelines for implementation of cystic fibrosis newborn screening programs: Cystic Fibrosis Foundation workshop report. Pediatrics, 2007.PMID 17272609
- [9]Dijk FN, Fitzgerald DA. The impact of newborn screening and earlier intervention on the clinical course of cystic fibrosis. Paediatr Respir Rev, 2012.PMID 23069119
- [10]Farrell PM, Kosorok MR, Laxova A, et al. Nutritional benefits of neonatal screening for cystic fibrosis. Wisconsin Cystic Fibrosis Neonatal Screening Study Group. N Engl J Med, 1997.PMID 9395429
- [11]LeGrys VA, Yankaskas JR, Quittell LM, et al. Diagnostic sweat testing: the Cystic Fibrosis Foundation guidelines. J Pediatr, 2007.PMID 17586196
- [12]De Boeck K. Cystic fibrosis in the year 2020: A disease with a new face. Acta Paediatr, 2020.PMID 31899933