Diagnosis: Cystic Fibrosis: Diagnostic Tests
• Immunoreactive trypsinogen measurement, along with DNA testing, is used to screen newborns for cystic fibrosis sis. A positive result requires confirmation by sweat chloride testing.
• The Cystic Fibrosis Foundation requires that quantitative sweat chloride measurements be used to confirm the diagnosis of cystic fibrosis. A sweat chloride level of 60 mmol/Lor greater is suggestive of cystic fibrosis. A chloride level between 40 and 59 mmol/L is an intermediate level and a chloride level of 39mmol/L or less is considered normal.
• The Cystic Fibrosis Foundation suggests that two positive sweat chloride results be obtained to confirm the diagnosis of cystic fibrosis. An initial positive sweat chloride result should trigger the collection of another sweat sample and measurement of sweat chloride.
• Almost all children with cystic fibrosis (99%) have elevated sweat chloride values.
• Serum chloride levels are usually normal in cystic fibrosis patients.
