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CF diagnostics

My 3 and half old son suffer of often breathing infects and long lasting cough.Usually dry cough time to time moist cough. Is possible to have CF when he went through a neonatal screening on CF in 2010 and chlorid swap test two years ago?. Both with negative results.our doctor advices to do chlorid test again. The result of the test was 20. Thanks
Dear questioner,
CF is an illness with dysfunctionning of a chloride channel in the cell membrane, resulting in viscous secretions affecting many organs of the body, but mainly the lung and the pancreas. The full picture with pancreatic insufficiency shows fatty, smelly stools and diarrhea, the child does not gain weight and does not grow properly. Some forms of CF do not have pancreatic insufficiency, so lung symptoms are the main ones, like chronic cough, increased mucus production, airway infections, often severe, such as pneumonia. If there is suspicion of CF, a sweat test is recommended. This test should be done in a certified and experienced CF center, using the so-called “pilocarpine ionotophoresis” to measure the chloride concentration in the sweat. If your son’s test has been performed like this, a value under 40 mmol/l chloride concentration is negative (40-60 mmol/l is borderline, over 60 mmol/l positive). Together with a negative neonatal screening (of course, theoretically falsely negative values are possible), CF can be excluded if the test was done correctly. For being on the safe side, one could of course do the test again (according to the mentioned standards) and if it shows a value in the same range as before, I would say, CF can be excluded.
You mention as symptoms that your son suffers from breathing infects and long lasting cough, here it is important to know, that little children have many airway infections per year (up to 8 times a year) and sometimes it is hard to distinguish, what is still in the normal range. Furthermore, besides CF, there are several reasons for chronic cough: bronchial asthma, allergies, reflux of gastric acid into the esophagus, germs, immue defects, structural abnormalities of the lung etc. that should also be looked for.
Best regards,
Dr. Daniela d’Alquen (Coordinator of the Central English Archive of ECORN-CF)