Cystic fibrosis (CF) is a genetic condition affecting multiple organs, primarily the lungs and digestive system. It is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which alters the body’s electrolyte transport system. This results in thick, sticky mucus that can clog airways and ducts in organs like the lungs, pancreas, and intestines. While historically diagnosed in infancy or early childhood, CF can also be identified in adulthood, sometimes presenting with different symptoms or a milder progression.
Reasons for Adult Testing
Adults might undergo testing for cystic fibrosis due to various clinical presentations. Chronic respiratory issues, such as persistent cough, wheezing, recurrent lung infections, and shortness of breath, often prompt investigation. Digestive problems also serve as indicators, including chronic diarrhea, abdominal pain, difficulty gaining weight, or pancreatitis.
Some adults may seek testing due to a family history of CF, especially if a relative has been diagnosed or is a known carrier. Male infertility, specifically congenital bilateral absence of the vas deferens (CBAVD), is another common reason for adult CF diagnosis, as it can be a manifestation of CFTR dysfunction.
For individuals born before widespread newborn screening programs, symptoms might go unnoticed until later in life, leading to an adult diagnosis.
Primary Diagnostic Methods
The primary diagnostic approach for cystic fibrosis in adults involves a combination of a sweat chloride test and genetic testing. The sweat chloride test measures the amount of chloride in sweat, which is elevated in individuals with CF. This test involves applying pilocarpine and a mild electrical current to a small skin area to stimulate sweat production.
After about five minutes of stimulation, sweat is collected for approximately 30 minutes. The collected sweat is then analyzed for its chloride concentration. A sweat chloride concentration of less than 30 mmol/L makes a CF diagnosis unlikely. Values between 30 and 59 mmol/L are intermediate and require further assessment. A concentration of 60 mmol/L or greater supports a diagnosis of CF.
Genetic testing, or DNA analysis, identifies mutations in the CFTR gene. More than 2,000 different mutations have been linked to CF. Genetic tests can include targeted mutation panels, which check for common CF-causing mutations, or full gene sequencing, which examines the entire CFTR gene for less common mutations. Genetic testing complements the sweat test, especially in cases with intermediate sweat chloride results or a family history of CF.
Interpreting Test Outcomes
Understanding the results from cystic fibrosis testing involves evaluating both sweat chloride and genetic analyses. A high sweat chloride reading (60 mmol/L or greater), combined with identification of two CF-causing mutations in the CFTR gene, confirms a diagnosis of cystic fibrosis.
Conversely, normal sweat chloride levels (less than 30 mmol/L) and the absence of CF-causing mutations mean that cystic fibrosis is unlikely. Clinical symptoms and family history are also considered.
Intermediate sweat chloride results (30 to 59 mmol/L), or the identification of only one CFTR mutation, suggest an uncertain outcome. In such scenarios, additional testing, such as comprehensive genetic sequencing or other specialized functional tests, may be necessary to clarify the diagnosis. These results might indicate a milder form of CF or a CFTR-related disorder. Individuals with one CFTR mutation but no symptoms are considered carriers; they do not have CF but can pass the mutation to their children.
What Happens After Testing
Following a cystic fibrosis diagnosis, or even with uncertain results, consultation with a CF specialist is a key next step. These specialists can provide comprehensive evaluation and guide subsequent care. They help interpret test results within the context of an individual’s symptoms and health history.
Genetic counseling is also recommended for individuals diagnosed with CF and their families, as well as for carriers. A genetic counselor can explain CF inheritance patterns, discuss family planning implications, and provide information on carrier testing for other family members. This counseling helps individuals make informed decisions about their health and reproductive options.
A comprehensive clinical evaluation often follows testing, regardless of the outcome. This evaluation helps to understand the full clinical picture, assess organ involvement, and rule out other conditions that might mimic CF symptoms. This assessment lays the groundwork for any necessary monitoring or management plans, focusing on the individual’s specific health needs.