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Cystic Fibrosis

Could it be something else?



I have not felt all that well for a few years. Recently, my ENT finally sent me to a CF center and I did the sweat test. They did each arm and results were positive with a 62 and 66. I`m 27 years old. Is it really likely that I have cystic fibrosis or could it be something else that causes a positive sweat test? If so, what other diseases/problems can cause those results?


The diagnosis of Cystic Fibrosis can indeed be made in adults. Approximately 7% of new diagnoses are in adults, based on information from the Cystic Fibrosis Foundation. Patients diagnosed with CF later in life overall have milder symptoms and atypical features, often referred to as "non-classic CF". It is not uncommon for patients diagnosed as adults to doubt the diagnosis when they compare their symptoms to those of "classic CF".

Diagnosis is based on two criteria:

1. Evidence of disease.  This can be the classic pulmonary disease or more subtle findings. Sinus disease is one of the typical findings in CF. Others include gastrointestinal symptoms such as pancreatitis, infertility, digital clubbing (a change in fingernails), mild asthma-like symptoms...

2. Evidence of abnormal chloride transport. This can be confirmed by sweat testing, genetics testing or nasal potential differences (a primarily research technique). Neonatal screening diagnosis is now also included.

Sweat chloride should be performed at a CF Foundation accredited center as less experienced labs may result in inaccurate results. The diagnosis of CF relies on a sweat chloride greater than 60 on 2 separate occasions (not 2 arms at the same occasion).

There are conditions that may have a false positive. Some findings that have been identified include:

Of these options, many of which are rare with findings that are not easily confused with CF, CF is relatively common. It is reasonable, based on a positive sweat chloride, to see an adult CF specialist who can help sort out the diagnosis. A CF Care Center can be located through the CF Foundation's website, http://www.cff.org.

For more information:

Go to the Cystic Fibrosis health topic, where you can:

Response by:

Patricia   Joseph, MS, MD Patricia Joseph, MS, MD
Associate Professor of Medicine
College of Medicine
University of Cincinnati