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How is cystic fibrosis diagnosed?

Family history, persistent respiratory disease, or clinical evidence of pancreatic insufficiency may suggest the diagnosis of cystic fibrosis. Screening for pancreatic insufficiency is done by measuring the levels of two enzymes in the stool. This test is not as reliable as measuring the sweat chloride level. Lung function testing can identify certain abnormalities in the way the

lungs and airways work. These abnormalities may be caused by problems other than cystic fibrosis.

The most common test for cystic fibrosis is called the sweat test. The sweat test is both the easiest and most accurate test for cystic fibrosis. It measures the amount of salt (sodium chloride) in the sweat. In this test, an area of the skin (usually the forearm) is made to sweat by using a chemical called pilocarpine and applying a mild electric current. To collect the sweat, the area is covered with a gauze pad or filter paper and wrapped in plastic. After 30 to 40 minutes, the plastic is removed, and the sweat collected in the pad or paper is analyzed. Higher than normal amounts of sodium and chloride suggest that the person has cystic fibrosis.

Immunoreactive trypsinogen test (IRT) is a blood test which measures the level of immunoreactive trypsinogen, which is generally higher in babies with cystic fibrosis than those without it. This test gives many false positive results immediately after birth, and so requires a second test several weeks later. A second positive result is usually followed by a sweat test. In the IRT test, blood drawn 2 to 3 days after birth is analyzed for a specific protein called trypsinogen. Positive IRT tests must be confirmed by sweat and other tests.
A genetic test is done if a patient’s sweat test is negative and there is still high suspicion that the patient has cystic fibrosis. A genetic test, also known as a genotype test or mutation analysis, is designed to analyze DNA for the presence of one of the several hundred mutations that can cause cystic fibrosis. The test involves collecting a sample of the patient’s blood. The test cannot detect all of the mutations that can cause cystic fibrosis, however, so its sensitivity is only about 80% to 85%. Genetic testing cannot be used to predict the severity of symptoms. There is no way to know, based on a person’s genotype, whether cystic fibrosis will be fatal or mild.

Chest x-ray findings may aid in diagnosis. Hyperinflation and bronchial wall thickening are the earliest findings. Subsequent changes include areas of infiltrate, atelectasis, and hilar adenopathy. With advanced disease, segmental or lobar atelectasis, cyst formation, bronchiectasis, and pulmonary artery and right ventricular enlargement occur. Branching, fingerlike opacifications that represent mucoid impaction of dilated bronchi are characteristic. In almost all cases, sinus x-rays and CT studies show persistent opacification of the paranasal sinuses.

A small percentage of people with cystic fibrosis have normal sweat chloride levels. They can only be diagnosed by chemical tests for the presence of the mutated gene.

More information on cystic fibrosis

What is cystic fibrosis? - Cystic fibrosis is a hereditary disease of the exocrine glands. Cystic fibrosis affects the pancreas and the glands that secrete sweat and mucus.
What causes cystic fibrosis? - Cystic fibrosis is caused by a defect in the person's genes. The defective gene that is responsible for causing cystic fibrosis is on chromosome 7.
What're the complications of cystic fibrosis? - Most people with cystic fibrosis also have digestive problems. People with cystic fibrosis have an increased risk of lung infections.
What're the symptoms of cystic fibrosis? - The symptoms of cystic fibrosis usually develop during early childhood. Cystic fibrosis is characterized by the production of very thick and sticky mucus.
How is cystic fibrosis diagnosed? - Family history, persistent respiratory disease, or clinical evidence of pancreatic insufficiency may suggest the diagnosis of cystic fibrosis.
What's the treatment for cystic fibrosis? - Treatment for cystic fibrosis consists of the intake of digestion enzymes, nutritional supplements, percussion and postural drainage of the lungs, improved antibiotics.
What cystic fibrosis medications are available? - Cystic fibrosis medications include H2 receptor antagonists, oral corticosteroids, ibuprofen, erythromycin, amoxicillin-clavulanate, etc.
What cystic fibrosis diet is suggested? - People with cystic fibrosis usually require high-calorie diets and vitamin supplements. Most people with cystic fibrosis need to take pancreatic enzymes.
What's the gene therapy for cystic fibrosis? - Gene therapy for cystic fibrosis typically aims to supplement a defective mutant allele with a functional one.
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