Unifying Concepts

Diagnostic Criteria for Cystic Fibrosis

Cystic Fibrosis (CF) is a multisystem disorder caused by mutations in the gene for the CF transmembrane conductance regulator (CFTR), which encodes an ion channel protein, with more than 2000 mutations identified to date. A diagnosis of CF initially relied on phenotype, with clinical recognition of characteristic signs and symptoms.

Diagnostic Criteria for Cystic Fibrosis

BOTH of the following criteria must be met to diagnose cystic fibrosis (CF):

  • Clinical symptoms consistent with CF in at least one organ system, or positive newborn screen or genetic testing for siblings of patients with CF


  • Evidence of cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction (any of the following):
    • Elevated sweat chloride ≥60 mmol/L
    • Presence of two disease-causing variants in CFTR, one from each parental allele
    • Abnormal nasal potential difference

The accuracy of sweat chloride and nasal potential difference measurements are operator-dependent, so it is critical that testing be performed in experienced centers, following standard guidelines.



  1. Farrell PM, White TB, Ren CL, Hempstead SE, Accurso F, Derichs N, Howenstine M, McColley SA, Rock M, Rosenfeld M, Sermet-Gaudelus I, Southern KW, Marshall BC, Sosnay PR. Diagnosis of Cystic Fibrosis: Consensus Guidelines from the Cystic Fibrosis Foundation. J Pediatr. 2017 Feb;181S:S4-S15.e1. [Medline]
  2. Castellani C, Duff AJA, Bell SC, Heijerman HGM, Munck A, Ratjen F, Sermet-Gaudelus I, Southern KW, Barben J, Flume PA, Hodková P, Kashirskaya N, Kirszenbaum MN, Madge S, Oxley H, Plant B, Schwarzenberg SJ, Smyth AR, Taccetti G, Wagner TOF, Wolfe SP, Drevinek P. ECFS best practice guidelines: the 2018 revision. J Cyst Fibros. 2018 Mar;17(2):153-178. [Medline]


Created Feb 27, 2020.

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