Sweat Chloride

Cystic Fibrosis Testing based on clinical suspicion
Newborns (after age 48 hours)
1. Newborn Screening positive for 2 CF mutation (confirmation)
2. Newborn Screening positive for 1 CF mutation
Ultra-high immunoreactive trypsinogen positive
Presentations possibly consistent with CF (despite negative Newborn Screening)
1. Poor weight gain, Failure to Thrive or Malnutrition
2. Growth Delay
3. Digital Clubbing
4. Chronic respiratory symptoms
  1. Cough, Wheezing or Shortness of Breath
  2. Recurrent respiratory or sinus infections
  3. Nasal Polyposis in children
5. Chronic gastrointestinal symptoms
  1. Steatorrhea or frequent bulky stools

Sweat Glands in Cystic Fibrosis secrete a salty fluid with high chloride concentrations

Obtain Sweat Chloride test at Cystic Fibrosis Foundation accredited lab
Minimum sweat amount required: 50 mg (200 mg better)
Quantitative Pilocarpine Iontophoresis
1. Stimulates local sweat production (parasympathetic)
2. Collect sweat on gauze pads
3. Analyze Sodium and chloride content
Validity
1. Difference between Sodium and chloride >30 meq/L suggests an invalid test

Sweat Chloride >= 60 mmol/L (or meq/L)
1. Consistent with Cystic Fibrosis (refer as if 2 CF mutations)
Sweat Chloride <= 29 mmol/L (or meq/L)
1. Cystic Fibrosis is unlikely
Sweat Chloride 30 to 59 mmol/L (or meq/L)
1. Intermediate for CF
2. Consult with local CF center
3. Consider repeat Sweat Chloride, Genetic Testing or evaluation at CF center