Cystic Fibrosis

Reproductive

Report in 72Hrs

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No Fasting Required

Details

Genetic test or sweat chloride test.

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Cystic Fibrosis Test Information Guide

Why is it done?
- Detection and diagnosis of cystic fibrosis, a genetic disorder affecting mucus-producing glands in the lungs, pancreas, and digestive system
- Newborn screening programs performed on all newborns within 24-48 hours of birth to identify CF early
- Diagnostic testing in infants and children presenting with respiratory symptoms (chronic cough, recurrent pneumonia) or gastrointestinal symptoms (failure to thrive, fatty stools)
- Genetic counseling and carrier screening for family members of CF patients or couples planning pregnancy
- Confirmation of suspected CF diagnosed through elevated immunoreactive trypsinogen (IRT) on newborn screening
Normal Range
- Sweat Chloride Test (Gold Standard): Normal (Negative): <30 mmol/L - Rules out CF diagnosis Borderline: 30-59 mmol/L - Repeat testing recommended Positive (CF diagnosis): ≥60 mmol/L - Consistent with CF diagnosis
- Immunoreactive Trypsinogen (IRT) - Newborn Screening: Normal (Negative): <110 ng/mL or lab-specific cutoff - CF unlikely Elevated: >110 ng/mL or above lab cutoff - Warrants confirmatory testing (may indicate CF or pancreatic insufficiency)
- Genetic Testing (CFTR Gene Mutations): Normal: No CF-causing mutations detected Carrier: One CF mutation identified (heterozygous - not affected) Affected: Two CF mutations identified (homozygous or compound heterozygous - CF diagnosis confirmed)
- Nasal Potential Difference (NPD): Normal: <-5 mV Abnormal (suggestive of CF): ≤-5 mV (alternative diagnostic test)
Interpretation
- Diagnostic Criteria (per CF Foundation):
  - Sweat chloride ≥60 mmol/L PLUS clinical symptoms OR positive family history OR positive newborn screening
  - Two CF-causing CFTR mutations identified (genetic testing)
  - Sweat chloride 30-59 mmol/L PLUS abnormal nasal potential difference
- Test Results Interpretation:
  - Sweat Chloride <30 mmol/L: CF is very unlikely; diagnosis ruled out in most cases
  - Sweat Chloride 30-59 mmol/L: Borderline; repeat sweat test recommended or additional testing (genetic analysis, NPD) needed
  - Sweat Chloride ≥60 mmol/L: Diagnostic of CF when combined with clinical features or confirmed by genetic testing
  - Two CFTR Mutations (Genetic Test): Confirms CF diagnosis regardless of sweat chloride results
  - One CFTR Mutation: Carrier status; genetic counseling recommended for family members
- Factors Affecting Results:
  - Patient age and hydration status (sweat test should be performed when child is >2 weeks old)
  - Eczema or skin conditions affecting sweat collection sites
  - Inadequate sweat sample collection or poor technique
  - CFTR mutation type (some mutations produce variable phenotypes)
Associated Organs
- Primary Organ Systems Affected:
  - Respiratory System (Lungs): Thick mucus accumulation causing chronic infections, bronchiectasis, and progressive lung disease
  - Pancreas: Ductal obstruction leading to exocrine pancreatic insufficiency (fat malabsorption) and endocrine dysfunction (CF-related diabetes)
  - Gastrointestinal Tract: Meconium ileus in newborns, distal intestinal obstruction syndrome (DIOS), and cirrhosis
  - Hepatobiliary System: Secondary biliary cirrhosis and portal hypertension (10-15% of CF patients)
- Associated Medical Conditions:
  - Chronic bacterial airway infections (Pseudomonas aeruginosa, Burkholderia cepacia, Staphylococcus aureus)
  - Bronchiectasis and progressive lung damage
  - CF-related diabetes mellitus (CFRD)
  - Pancreatic insufficiency with nutrient malabsorption
  - Allergic bronchopulmonary aspergillosis (ABPA)
  - CF-related liver disease and cirrhosis
  - Sinusitis and nasal polyposis
  - Cystic fibrosis-related bone disease (osteoporosis)
- Potential Complications of Abnormal Results:
  - Respiratory failure and need for mechanical ventilation
  - Failure to thrive and growth impairment in children
  - Hemoptysis (coughing blood) from bronchial vessel erosion
  - Pneumothorax (collapsed lung)
  - Need for lung transplantation in advanced disease
Follow-up Tests
- Confirmatory Testing (if initial CF test positive):
  - Repeat sweat chloride test (within 2 weeks) if borderline results (30-59 mmol/L)
  - Comprehensive CFTR gene sequencing and deletion/duplication analysis for definitive diagnosis
  - Nasal potential difference (NPD) testing if sweat test results inconclusive
- Initial Assessment Tests (upon CF diagnosis):
  - High-resolution chest CT or chest X-ray to assess baseline pulmonary function and degree of lung damage
  - Spirometry and pulmonary function tests (PFTs) to measure lung function (FEV1, FVC)
  - Fecal elastase-1 test (normal >200 mcg/g) to assess pancreatic enzyme secretion
  - Blood glucose or oral glucose tolerance test to screen for CF-related diabetes
  - Liver function tests and abdominal ultrasound to assess for CF-related liver disease
  - Fat-soluble vitamin levels (A, D, E, K) given risk of malabsorption
  - Nutritional assessment and biochemical markers (albumin, prealbumin)
- Ongoing Monitoring and Surveillance:
  - Pulmonary function tests (spirometry): Performed at least quarterly or more frequently if decline noted
  - Sputum culture and airway microbiology studies to monitor for new pathogenic organisms
  - Annual glucose tolerance testing and hemoglobin A1C to screen for CF-related diabetes
  - Periodic liver function assessment and ultrasound for cirrhosis screening
  - DEXA scan for bone density assessment (baseline and follow-up) due to osteoporosis risk
  - Annual chest X-ray or high-resolution CT to monitor for progression of bronchiectasis
- Genetic Counseling & Family Testing:
  - Carrier screening for siblings and extended family members of confirmed CF patients
  - Genetic counseling for parents regarding recurrence risk (25% for each pregnancy if both parents are carriers)
  - Prenatal/preimplantation genetic testing for family planning
Fasting Required?
- Sweat Chloride Test: NO fasting required - Can eat and drink normally before the test
- Genetic Testing (Blood Sample): NO fasting required - Can eat and drink normally
- Immunoreactive Trypsinogen (IRT) - Newborn Screening: NO fasting required (performed in newborns)
- Oral Glucose Tolerance Test (associated screening): Fasting 8-10 hours required before initial glucose draw
Special Preparation Instructions:
- Sweat Test: Arrive well-hydrated; avoid lotions or creams on forearms 24 hours prior; wear loose clothing; avoid strenuous activity before test
- Temperature: Perform when room temperature is 18-27°C (sweat production is temperature-dependent)
- Age: Sweat test preferably performed when patient is at least 2 weeks old (insufficient sweat production in very young neonates)
- Medications: No medications need to be held; inform provider of any recent antibiotics or medications
- Skin Conditions: Ensure forearms are free of eczema, rashes, or broken skin for test site
- Newborn Screening: Usually collected on heel stick from newborn infant at 24-48 hours of age (standard of care)

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