Lab
Sweat Chloride
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Sweat Chloride
, Sweat Test
See Also
Delta F508
Indications
Cystic Fibrosis
Testing
Newborn Screening
positive for 2 CF mutation (confirmation)
Newborn Screening
positive for 1 CF mutation
Ultra-high immunoreactive trypsinogen positive
Presentations possibly consistent with CF (despite negative
Newborn Screening
)
Poor weight gain,
Failure to Thrive
or
Malnutrition
Growth Delay
Digital Clubbing
Chronic respiratory symptoms
Cough
,
Wheezing
or
Shortness of Breath
Recurrent respiratory or sinus infections
Nasal Polyp
osis in children
Chronic gastrointestinal symptoms
Steatorrhea or frequent bulky stools
Technique
Obtain Sweat Chloride test at
Cystic Fibrosis
Foundation accredited lab
Minimum sweat amount required: 50 mg (200 mg better)
Quantitative
Pilocar
pine
Iontophoresis
Stimulates local sweat production (parasympathetic)
Collect sweat on gauze pads
Analyze
Sodium
and chloride content
Validity
Difference between
Sodium
and chloride >30 meq/L suggests an invalid test
Labs
Interpretation
Sweat Chloride >= 60 mmol/L (or meq/L)
Consistent with
Cystic Fibrosis
(refer as if 2 CF mutations)
Sweat Chloride <= 29 mmol/L (or meq/L)
Cystic Fibrosis
is unlikely
Sweat Chloride 30 to 59 mmol/L (or meq/L)
Intermediate for CF
Consult with local CF center
Consider repeat Sweat Chloride,
Genetic Test
ing or evaluation at CF center
Causes
False Positive
Tests
Glucose 6 Phosphate Dehydrogenase
deficiency (
G6PD
)
Hypothyroidism
Glycogen Storage Disease
Untreated
Adrenal Insufficiency
Malnutrition
Reference
Bakerman (1984) ABC's of Lab Data, ILD, Greenville, NC
Collins (2024) Am Fam Physician 109(5): 388-90 [PubMed]
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