The key for the physician to come to an accurate diagnosis of CF is to take a careful history and to listen to clues of a family history of CF, to problems in early childhood and to recognize the pattern of symptoms mentioned before.
Cystic fibrosis testing consists of ordering a sweat test, which is easy to do and gives a reliable diagnosis (more than 60 mEq/L of chloride in sweat is diagnostic for CF). There are also more elaborate (and more expensive) genetic tests available like the polymerase chain reaction to identify the presence of the CFTR gene of CF. These would be done when the sweat gland test yields borderline values. Other tests that the physician or pediatrician would order is a pulmonary function test, which shows low oxygen levels in the blood (hypoxemia), a reduced forced vital capacity (FVC) and a reduced forced respiratory volume in 1 second (FEV1).
This may all sound very technical, but behind these numbers is an exact description and measurement of the function of the lung of the patient with cystic fibrosis (CF). The limitations of the lungs to transport oxygen into the circulatory system is what dictates the patient’s symptoms, how much the patient has to suffer and also what the future life expectancy will be. Other tests that the physician may use are chest X-rays and CT scans to look at the condition of the lungs and sinuses. Specific other tests are done depending on what the clinical condition demands.
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2. National Asthma Education and Prevention Program. Expert Panel Report II. National Heart, Lung and Blood Institute, 1997.
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