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Diagnosis of CF

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.

 Diagnosis of CF (Pulmonary Function Study)

Diagnosis of CF (Pulmonary Function Study)



1. Noble: Textbook of Primary Care Medicine, 3rd ed., Copyright © 2001 Mosby, Inc.

2. National Asthma Education and Prevention Program. Expert Panel Report II. National Heart, Lung and Blood Institute, 1997.

3. Rakel: Conn’s Current Therapy 2002, 54th ed., Copyright © 2002 W. B. Saunders Company

4. Murray & Nadel: Textbook of Respiratory Medicine, 3rd ed., Copyright © 2000 W. B. Saunders Company

5. Behrman: Nelson Textbook of Pediatrics, 16th ed., Copyright © 2000 W. B. Saunders Company

6. Merck Manual: Cystic fibrosis (thanks to for this link)

7. Goldman: Cecil Textbook of Medicine, 21st ed., Copyright © 2000 W. B. Saunders Company

8. Ferri: Ferri’s Clinical Advisor: Instant Diagnosis and Treatment, 2004 ed., Copyright © 2004 Mosby, Inc.

9. Rakel: Conn’s Current Therapy 2004, 56th ed., Copyright © 2004 Elsevier

Last modified: November 10, 2014

This outline is only a teaching aid to patients and should stimulate you to ask the right questions when seeing your doctor. However, the responsibility of treatment stays in the hands of your doctor and you.