ADVANTAGES AND DISADVANTAGES OF TEST | |||
---|---|---|---|
TEST | POSITIVE RESULTS FOR CF | ADVANTAGES | DISADVANTAGES |
Sweat chloride levels | ≥ 60 mmol/L indicative of CF ≤ 39 mmol/L unlikely to be CF 40–59 mmol/L considered intermediate | A high sweat chloride level is very strong evidence for CF | It is possible to have CF and intermediate or low sweat chloride levels; intermediate levels are common in atypical CF and require repeat sweat chloride level testing or further testing of NPD or genetic analysis |
NPD | ≥30 mV suggestive of CF Relevant response to zero-chloride perfusate with isoproterenol might help rule out CF | Can add strength to diagnosis of atypical CF or help rule out CF | Not definitive for diagnosis alone owing to overlap between normal values and values in CF |
Genetic analysis | Presence of 2 CFTR gene mutations known to cause disease in trans arrangement on 2 separate chromosomes (cis arrangement on the same chromosome is not associated with disease) | Identification of 2 known CFTR gene mutations provides strength to diagnosis | Up to 15% of individuals with CF have rare or unidentified CFTR gene mutations |
CF—cystic fibrosis, CFTR—cystic fibrosis transmembrane receptor, NPD—nasal potential difference.