Cystic Fibrosis: Diagnosis

Signs and symptoms of cystic fibrosis primarily reflect respiratory and intestinal involvement.

Respiratory problems include:

Frequent cough, which is dry at first, subsequently becoming productive, and may contain blood due to bronchiectasis.

Infections of the bronchi, which can occasionally evolve into secondary bronchopneumonia associated with increased risk of pulmonary abscess or pleurisy.

Recurrent respiratory infections, which are associated with Staphylococcus aureus and Pseudomonas aeruginosa infections in particular.

Other respiratory problems such as wheezing, dyspnea, pneumothorax, sinusitis and/or nasal polyposis, and mild cyanosis, which may be generalized or of the lips and extremities.

Intestinal involvement may lead to:

Bowel obstruction, with meconium ileus and intussusception are particularly common at birth. Other digestive symptoms are steatorrhea, frequent vomiting, rectal prolapse, liver disease, and cystic fibrosis-related diabetes.

Malabsorption, which causes failure to thrive, retarded growth, and fatigue.

Male infertility is also a symptom. Men nearly always have azoospermia due to congenital bilateral absence of the vas deferens.

Women may have some abnormalities of the cervical mucus, but fertility does not appear to be significantly reduced in the absence of severe malnutrition.

Cystic fibrosis is diagnosed by a sweat test (which can be done as early as 48 hours of age). A positive sweat test (see below), combined with pulmonary and/or gastrointestinal symptoms, establishes the classic diagnosis in nearly all cases. CF mutations, identified through genetic testing, can also confirm diagnosis, or they can be used to make the diagnosis in patients with mild forms of the disease.

A patient with the symptoms and/or signs presented above may require the following tests:

• Sweat test: Most patients with CF have chloride values between 60 and 110 mEq/L.
• Genetic testing: Patients with a family history of CF, and those who exhibit signs and symptoms, but do not have a positive sweat test, should have a genetic test. Prenatal testing and newborn screening may be used. Early detection renders a better clinical course.
• Stool tests: Fecal fat analysis can be used to confirm pancreatic insufficiency.