How is cystic fibrosis diagnosed?

Early detection of the signs and symptoms of cystic fibrosis can be pivotal, since this affords valuable time to manage and mitigate future damage caused by the condition’s progression. Although cystic fibrosis can present at any point in the lifespan, it is commonly identified early in life. Clinical manifestations of cystic fibrosis may be confirmed by a sweat test revealing a high concentration (>60 mEq/L) of sweat chloride.^[1][2] Sweat electrolyte levels are raised in the presence of cystic fibrosis, since the condition raises concentrations of sodium and chloride.^[3]

Cystic fibrosis can be detected as early as gestation: families that may be genetically predisposed to the condition can undergo amniocentesis (pre-birth genetic testing). After delivery, the presence of bowel obstructions or a positive test on the Guthrie blood spot test (which tests for increased pancreatic immune activity) can both indicate that a newborn may have cystic fibrosis. In infancy and early childhood, recurring respiratory distress with cough, wheezing, and/or pneumonia plus a failure to thrive (due to pancreatic insufficiency, present in 85-90% of cystic fibrosis cases) is another set of clinical warning signs.^[3] Through childhood and even adulthood, continuing respiratory symptoms, nasal polyps, sinusitis, and congenital absence of the vas deferens (in males) can also signal the presence of cystic fibrosis.^[1][3]

Other tests that might be used in diagnosis include: nasal potential difference testing (with results in alignment with cystic fibrosis) and genetic testing for the presence of pathogenic CFTR variants. Gut malabsorption can indicate that pancreatic function is suffering due to cystic fibrosis; this is tested by measuring fecal elastase. Low levels of fecal elastase suggest pancreatic insufficiency and, likely, malabsorption.^[2]