What is Involved in Making a Diagnosis of Cystic Fibrosis?

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  • Written By: M.C. Huguelet
  • Edited By: Heather Bailey
  • Last Modified Date: 18 October 2019
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Cystic fibrosis is a genetic disorder which causes bodily secretions such as mucus and digestive fluid to be sticky and thick. Since these thick secretions are not easily vacated by the body, they build up in the organs, causing such complications as chronic lung infections and lung damage as well as poor nutrient absorption. An early diagnosis of cystic fibrosis followed by ongoing treatment can significantly improve the life expectancy of an individual with the condition. Making a diagnosis of cystic fibrosis usually involves a combination of blood and sweat tests and, in some cases, genetic testing. Advances in genetic testing now allow cystic fibrosis to be identified even in unborn babies.

In some countries, such as the United States, every newborn is screened for cystic fibrosis via blood test shortly after birth. After a blood sample has been taken, it is examined for evidence of a digestive chemical called immunoreactive trypsinogen (IRT), which is normally present in high concentrations in the blood of cystic fibrosis sufferers. If a high IRT concentration is detected, further testing is usually performed to confirm a diagnosis of cystic fibrosis.


Among newborns whose blood shows a high IRT concentration, a sweat test is often used to confirm a diagnosis of cystic fibrosis. The genetic defect which causes this condition inhibits the body’s ability to transport salt in and out of the cells. As a result, those with cystic fibrosis tend to have very salty sweat. During a sweat test, a patch of skin is rubbed with a chemical that stimulates sweating, and the sweat produced is then absorbed with a strip of paper. If the paper shows that the sweat contains a large amount of salt, a diagnosis of cystic fibrosis may be made.

Should the results of a sweat test prove inconclusive, physicians may recommend genetic testing to verify a diagnosis of cystic fibrosis. During genetic cystic fibrosis testing, a blood sample is drawn and then sent to a laboratory, where the genes found within it are studied for evidence of the defect which causes the disorder. In addition to being used to confirm cystic fibrosis following ambiguous sweat test results, genetic testing may also be performed on unborn babies who have a heightened risk of the condition. Babies considered to be at high risk for developing the condition are those whose parents are both carriers of the cystic fibrosis gene.


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